Here's my final set up and build details

Shimano GRX di2 11 speed,
GRX brakes
46-11 cassette
XT derailleur
46t Stone chainring on rotor 3d30 cranks
Carbonal gravel wheels with 29mm internal
Specialized Terra , 47mm measured at 50mm
Bontrager RSL 35/38 cm bars
Look S track pedals
Deda zero1 stem
Pro Falcon saddle
Leyzene cages

Here's another picture from a different angle

Thanks for the replies

I sorted out the 1x chainring issue with a Stone zero offset chainring.I'm really impressed with the quality and finish and it came with what look like chainring bolts specific to the chainring as when I tried to use them on my CX bike with another chainring they were too long. I've still got to shorten the chain a little bit and fine tune the chainset sitting but it handled a hard hilly ride while not optimal with any issues and slipping.

I've also upgraded the wheels and got a set of 29mm internal wheels from Carbonal which has bumped up the 47mm specialized Tracers I use to 51/52mm I do like the monster truck vibes but I may have to look into downsizing to the new 45mm tracers if there's any tyre rub

There is a minimum 5mm of space all round with the 47mm tracers which is plenty for fire-track roads and far more space than I had on my TCX with 42mm pathfinder tyres in and they worked perfectly without any clogging issues

From my experience of muddy CX races if the course is claggy it really doesn't matter how much space you have between the tyre and frame, mud will fill it eventually

I don't know how tall you are but I'm 179cm and set my saddle height at 75cm from the centre of the BB.

I have a 54cm and there is still plenty of seatpost left to raise the height if needed.

The tip of the stealth saddle is 5-6cm behind the BB which lets me get into a decently aggressive position, there is still a bit of room to move it forwards or backwards.

I've still to settle on my reach but currently have a 11cm stem which isn't far off

I've not had chance to ride it off-road in the couple of months I've been riding it but with road wheels and 28mm tyres it feels great . Subjectively, maybe a little less responsive than my road bike but it is definitely more compliant and it's no slower when comparing rides.

if you can it might be worth getting a bike fit on a jig and dialing in a position before committing to buying a frame as it sounds like you've been making various sized and styles of frames work.

One thing to take into consideration when measuring the stack is that you have have to add 10-20mm to take into account the headset cap for the internal routing or making space for the cables to enter the headset depending on the style you go for.

I fitted this token headset as it has seals aroung the cable entry ports,it adds 20mm or so to the stack height

https://www.orrobikes.com/product/token-cablebox-headset-semi-internal

hope that helps

There is quite a bit of info on the Graro thread

https://chinertown.com/index.php/topic,4766.30.html

I bought a Rotor T47 internal BB for mine and it works well with the Rotor 3D30 crank set and the ultegra derailleurs I fitted. I did have to space the crank out a little, I think the frame was designed around the GRX groupset which has a different offset

https://rotoruk.co.uk/v1.asp?prd=262149&cat=1054&ms1=GS1&gad_source=1&gclid=EAIaIQobChMI66iHo7KBiAMVKQ0GAB2kxB69EAQYASABEgIruPD_BwE

https://www.dyedbro.com/collections/gravel-all-road-frame-protection

Got it from R2 bike https://r2-bike.com/DYEDBRO-Gravel-Frame-Protection-Set-Stay-Free-matte-black

Thanks, that's just what I was looking for