After building several AR15s from 80% receivers I decided to try a 308 Win style AR build since the 308 ARs are not standardized so it would be more of a challenge. I purchased an Ares Armor "80% AR-10 DPMS .308", an interesting name because "AR-10" is trademarked by Armalite and uses a receiver with a flat cut on the rear whereas DPMS uses a curved receiver rear similar to the AR15. For the upper I got a Palmetto PA10 "modified DPMS" kit since I discovered the PA10 takedown pins would match the Ares locations on 6.880" centers.
Ares provides no information on machining their receiver so the 1st problem is where to locate the trigger group. Ares did drill out the selector indent hole which must match the location of the selector so the standard AR15 trigger group can be machined relative to the selector location.
After machining and assembly the following problems where discovered:
1) The PA10 takedown pins are too short by about 1/8" but are useable. I'll just make some proper pins.
2) The lower won't rotate on the front takedown pin. About .015" had to be filed off the lower to allow rotation.
3) The PA10 uses a roll pin to attach the bolt catch, the Ares uses a threaded pin. I made a pin from a 6-32 screw.
4) The bolt catch would not release the bolt. Apparently the PA10 catch is located out about 0.1" further. An AR15 catch works fine as does filing a chamfer on the PA10 catch so it doesn't hit the upper receiver OD.
5) The PA10 upper is tapered to AR15 width around the trigger group whereas the Ares lower is not. This is a non-critical 'looks' issue.
With these minor modifications the Ares lower mates nicely with the PA10 and fires flawlessly.