Well I don't have much to offer in the way of help but this sounds like a very cool project. I have been wondering why there have been no 6.8 SPC bolt guns. It is a completely respectable, 50 state deer cartridge. I have tactical shooting friends who swear by it for mulies and whitetails.
Recoil should be easy too. I would say leave the AR type barrels to ARs. The McGowan would probably serve you admirably. Best of luck with your project and update this thread with pics as you go!