I'm doing similar things. Some of the key features:
- AR15 grips
- More AR15-ish shaped mag well
- Rear drilled and tapped for ACE style stocks. Will have two positions to mount, high to put stock inline with barrel, and low to use stock irons (might not do this).
- nifty bolt release as mention
- AR15 safety
- Swiss Arms style take down pin (you know, the neat quick relase ones)
After the lower is done I hope to make a billet upper that is left side cocking lever with dust cover (cocking lever slot and ejection port), takes standard AR15 barrels (forends and rails fit also), flat top. Will have to do up a custom flat top gasblock too, might make it adjustable.
This is all on the drawing bored stuff right now. I hope to get started soon on the lower and have it sent to Dlask to have the magwell cut.