Hmm, looks like reamerrentals.com has 6.5 Grendel reamers. The ballistics look nice for an x39-length cartridge. Now to keep an eye out for a reasonably-priced 6.5 barrel.
Onlinemetals.com has 12x12" sheets of .063 4130 for $15.33+shipping.
I just realized the Hadar probably uses a slant-cut receiver since it's a Galil inside. I'll have to make a rear trunnion to fit.