You don't need tools to rebuild on a new lower.
It comes apart like any AR. You just need pin adaptors for the new pins to fit in the larger diameter pin holes on the old Colt M16 upper. Just hang onto the old buttstock, too, even the grip if you want total authentic and if it'll fit.
Tell him to order a new Stag lower and reuse all the rest of the parts, and order a new bolt carrier, bolt and pin adapters. It'll be like $160 for the assembled lower, $120 for a phosphate bolt assembly.
Nobody here is suggesting breaking a law, everyone is saying to abide by it. And once the reciever and bolt are destroyed, using the remaining parts is in full compliance with the law.
I've got a "government profile" AR built using a Colt/Martin Marietta 20" A2 upper probably from an early 80's M-16, a matching buttstock, DPMS chromed bolt and a Stag lower. It works fine.