Hello endo.alley,
Yes the 43.5mm for the two lower connections (front Frame and rear triangle) and the 31.85mm for the upper connection fits exactly between the Bearings. Before you cut tube you can measure it, by measuring the Bearing outside to outside and subtract 14mm. Than you are quite sure.
I have only one other problem (the rear shock absorber connection is 8x22mm not 8x30mm as in the description) with the Frame and i drove nearly 5000 up- ans downmeters since i build it. Also with little jumps (no big Air, this is not my game) and a lot of stony fields (S1-S3). I drove the SC Normad from a friend of me, and i think it works as fine as (the Normad is 650B i know, but in the home trail terrain this don‘t make a difference).
The FS830 is nearly per mm the same frame as the Pivot Firebird from 2019 (except of a longer Seattube) but don‘t have the superboost rear. But in my opinion it makes the Frame not as stiff and stressful.
So if you use high quality components (not as me Ztto Rotors and bottom braked, but i have exchanged both) i think you will get a great bike. I‘m thinking about building the same for my wife (but she says it isn‘t necessary