Not sure why you haven’t received any replies but my 2 cents: forget trying to re-use your old components. You probably won’t be able to find many *used* *frame only* FS bikes plus you’re cannibalizing one bike to build another (what will you do with the 8900 frame?). You’re also using parts that are up to 6 years old and there have been some pretty big advances since then in brakes, shifters, suspension, etc.
My advice? Sell the old to finance the new.
See that was my question. Have there been major advances? My current ride has full XTR, and Hayes Hydraulic disks.
I did just replace last year my stem and bars to a Easton Carbon riser bar.
But what has changed with the XTR derailers?
As far as not being able to find many frames, you are crazy. Go to Ebay, there are hundreds every day.