Are you using genuine Shimano adaptor?  It comes with the cup washers which you should be using when you install an adapter.  https://www.mtbdirect.com.au/shimano-post-frame-or-fork-to-post-caliper-brake-mount?brake-mount-size%09=117&option=340&gclid=EAIaIQobChMIw8H-r_nH7wIVPTVyCh0O5QApEAQYAiABEgIRzfD_BwE I'm using 160mm on the back without issue so far.

Re your seat post, is that photo looking up from the bb or down from the top?  I am using the 150mm post I linked and haven't had issues with it. Top of supplied seat clamp to saddle rails is 90mm when collapsed and 240mm when extended measuring along the line of the post. Will that work for you or not?  The collar of the post sits off the seat clamp but I don't remember if I could get it lower or if that was just where it worked for me, pretty sure I could get it lower but I can check for you if what I have measured sits too high for you.

Thanks for the response!

Yes.  Using that exact adapter with both cup washers.  I would assume that if you use the standard bolt from a 160 caliper mount or a 180 adapter that the holy length would be the same.  I ended up using a dremel with a cutting wheel and removing 1/8-1/4" from the end of each bolt and then successfully installing.  Don't love it but I think it will work.  I think some of the threads at the bottom of the insert may have been dirty or some other problem which restricted full required depth.

The photo is looking up from the bottom towards the seat clamp.  I bent the camera up 180 degrees, inserted from the top at the clamp and pushed down.

Mine is 250mm from clamp top to rails so about the same.  The bottom of the collar sit 50mm above the clamp and is far as it will insert.  If you measure the length of inserted seat post it is 160mm, which is where the tube obstruction is.  Full insertion to the post collar would be 210mm.  Lisa @ tantan said not to sand the ridge as that is where the two tubes are joined.  I am approx 20mm high form center of bottom bracket to top of saddle.  I am running 5mm shorter crane (170mm) so I am hopeful that I will just make it.  I would like to share with someone in my family that is shorter than me and why I am trying to figure it out.  Maybe I will need to switch to a 100mm or 125mm dropper to share.

Thanks.  What length.  Mine is a Reverb Stealth (SRAM) 150mm.  Tan Tan could have made the connection between the tubes smoother to accommodate dropper posts.  It doesn't start to curve until lower in the tube. 

Also attempted to mount the rear Shimano XT disc brake caliper using a 160->180 Shimano adapter and the mount holes are too shallow in the FM10.  .  The standard length Shimano bolts bottom out before becoming tight.  I don't enjoy my stuff being mickey mouse with extra washers and stuff to just make it work right.  These frames must not be proven or tested.  Each small issue I encounter makes me wonder how many people have encountered the same issues.

It also looks like I will need to get the aluminum spacers for mounting my DPX2 rear shock machined to increase the length of the reduced diamter portion that fits into the shock on either side as it is too wide as is.

Ran into another snag.  The 150mm SRAM Reverb Steak dropper post wont go in far enough.  I used a borescope and took this photo which shows some type of ridge at 160mm from the top of the seat post.  Looks like I should be able to sand.  I guess these are the challenges of buying a non-production frame.

Haha, thats crazy.  Had my morning coffee at Huxtons.  My buddy has a raised landcruiser with a big custom aluminum canopy on the rear for camping.  You might have seen him cruising around town.  Didn't venture in the water, but admired it from the hill.  Not sure my host warned me tho 

I ended up picking up some old stock new 29" XM421 with DT Swiss 350 last night.  $275.  Almost could not help myself.  ID 25mm which isnt ideal but it will be fine for a while.  Wasn't going to do it but then noticed that my buddy was riding ARC 24 on a SC 5010 with 2.5 tires and it has been working for the years that we have been riding together.  I wanted DT Swiss M1900 (ID 30mm) as they are good and reasonable, but everyone is out of stock.

I am not even sure what I going to do with this bike when I am done as I have a bike and my sons niner should be here soon.  Its like a tractor beam keeps pulling me in and making me build this bike. c-a-n-t  s-t-o-p.

So is there a preference on this frame for 27.5 or 29?  If you decide on 27.5 wheels (non-plus size) can you just get 165mm/170mm cranks and not have issues with pedal strikes?

I don't expect any change, that was posted over three months ago.

Also, after a fair bit of clarification,  I did get an answer out of them re the different options, no difference between the 27.5 and the 29 option.

Hello again. Can you please tell me what the difference between the 27.5 148 x 12 and 29er 148 x 12 frame actually is?  I want to run 27.5 plus tyres. Are they actually the same frame, does the 27.5 frame take plus tyres or do I need to order the 29er version?  Thank you.

Good morning, if you want to use 27.5 plus tyres, then you need to choose 27.5er frame
27.5er 148X12mm = 27.5er boost
15:19

So what dimensions are different from the 29er frame?
16:03

27.5*2.4 /27.5*2.6/37.5*2.8
29*2.35 tire
16:09

27.5*2.4 /27.5*2.6/27.5*2.8
16:54

Yes I know that. You list for sale both a 29 frame and 27.5 frame. I am asking you what dimensions on the two frames are different? Are chain stay or seat stay lengths different? Is the BB drop different? If they are identical frames why do you give both a 27.5 and 29 option?
17:07

The difference is that 142X12mm and 148X12mmaxle and tires can be installed in different sizes

Yes but you list both a 148mm x 12 27.5 AND a 148mm x 12 29er. What is the actual difference between these two frames?  Will a 29er wheel fit in the 27.5 plus frame?
17:17

27.5er frame can use 27.5er*2.4/2.6/2.8 tires
29er frame can only use 29er*2.35 tire
29er wheels are not suitable for 27.5 plus frame

So that must mean that the two frames have different dimensions. What dimensions are different?
17:24

I have asked my boss and he said that the size is universal
Therefore, the tire sizes of the 27.5er and 29er frames are both 27.5*2.4 /2.6/2.8 & 29*2.35
If you choose a 27.5er 148*12mm frame, you can use up to 27.5er*2.8 tires
If you choose 29er 148*12mm, you can use up to 29er*2.35 tires
29er wheels are  fit in the 27.5 plus frame

Thank you. I thought that was the case as it is with many of the big brand frames. I was just confused with the two listings. Thank you for checking.

Is it normal for Tan Tan to ship a carbon fiber rear axle?  Seems a bit sketch.  Doing some searching I didnt see where other were advocating a carbon fiber rear axle.

Fedex says the frame will be here on Friday .  There is a chance I may turn around and sell it.  Got a little impatient and bought my son a complete Niner rip 29 that should be here soon as well.  I am excited though as I have been reading this forum for a while and want to get my hands on a frame.