SPR's
Military ammo has cannelures to prevent bullet set-back. In bolt rifles, it is my understanding that bullets with cannelures are not generally used in their match ammo because cannelures may decrease the accuracy of the bullet. As far as semi-auto, while your theory would seem to make sense, althought I noticed in my testing absolutely no difference in multiple accuracy tests whether a round was hand fed one at a time. My experience has taught me sometimes in the field, theory and reality can be strangers. Again, I don't have any large mega-studies to cite, this was just my own personal experience as the same thing you mentioned had crossed my mind also.
You are correct about the A1 lowers, (mostly Colt, Diemco, and even a few Armalites) but lower receivers alone IMHO have little and or nothing to do with accuracy from all the articles I have read. Gene McMillian said it best about accuracy; Bullets, Bedding, & Barrel (not necessarily in that order and of course he was referring to bolt guns).
Ransom is known for their mechnical pistol rest and I understand it may be an industry standard for testing, haven't heard that much about the rifle rest they make. I do know the Lahti Mechanical Rest is used by many custom builders, and I bought it on the recommendation of reknowned sniper MAJ John Plaster, retired US Special Forces and author.
I would be interested in knowing more about the Mk12 Md 2 which you state is supposed to be more accurate if you have any info.
Regarding the review of the Angus Arms SPR, 3/4 MOA is respectable and my experience is a rack grade M16A2 is about 1.5 to 2 MOA so that's a big improvement.
What makes an SPR accurate? My opinion the ammo is the single biggest factor (not the FF barrel, although that is helpful).
As far your figures for just the rifle itself, if you want I can send you a complete list of suppliers. Again the total price for new parts for FFL holder is about $1800 and non-FFL holder is about $2200, without the Leupold optics. That may be cheaper depending on your SPR barrel (i.e, ADCO has complete Mk 12 Mod 0 uppers with White Oak barrels I think in the $1400 range, haven't checked lately).
If you decide to go forward with your SPR project, Gunners Mate I wish you the very best.