those are light and those aren't even the full R1s(notice RX on caliper) - full R1s are at 180ish and R1 racing closer to 150
Looking forward to pictures of your build.

That doesn't look right.
What derailleur is that?
Is it bottom pull?
Also, are the 256s supposed to have a high or low mount derailleur?

my build:
FSA SLK Compact double
weight 690g and price...from ebay 160.00
SEOlite cassette 11-36
weight 178g and 140.00
XTR M986 shadow + rear derailleur
weight 216 and price 128.00
XTR M980 shifters
weight 198 and price 110.00(for both)
bottom bracket (BB30)  56g (came with crank)
XTR M980 chain  260g and 40.00

My totals before n/w chainring and a 40 or 42 tooth:  weight  1598 and expense:  538.00

If I just go 1x - need a chainring was 45.00 at uptown...weight 2x chainrings total 117   1598-117=1481 + 31 = 1512g and price 583.00
For me...weight is same...price is much better....performance - unknown but doesn't match range

Stan's says seems to real general saying 3oz for first time and 2 oz after that.
I know I put 3/4 of a scoop on my 29er 2.0 tires and lose air over a few days - so I really should have put more to begin
Depending on tire size...bigger than 2.2 probably should do the 3oz to begin.

Just went and looked at Niner and their 'rules'

Do not exceed 40mm spacer stack height.
Do not place spacers above the stem. The stem must clamp the area
reinforced by the compression adjustment plug installed in step 5.1
Do not use tall crown races or place spacers under the crown race to
adjust head angle.
Do not grease the carbon steerer tube.

https://s3.amazonaws.com/NinerDocs/NIN_OWNERS_UNIVERS.pdf

I think the manufactures are limiting it to 40 or 50 with the thought of stem and bar on their putting a load....and to cover their butts.

There is a recommended height limit for spacers on a carbon steerer...40mm?

You can also get a shim so that your 27.2 seatpost works also if you like.

Interesting on the Hope discs and different.
What made you go with them?
At some point, hope you will give a review.