Assembling Grendel upper, would love any tips/tricks/info to help accuracy

[Hooz]

Sounds like you're on the right track. As for the receiver block, you'll need a DPMS Panther Claw type block...

http://www.bravocompanyusa.com/AR15-DPMS...20ar15.htm

You can find them cheaper other places, but that's what you need to look for.