Re: thermostat blank
Later model FEs didn't use an expansion tank, that was only the early versions. A 429 never used one, and as long as the radiator fill point is higher than the engine water level, that is fine. The radiator works fine for that
That being said, a thermostat is a great idea. I tend to drill a small hole, very small, 1/16 at the most, to allow water and air to pass while waiting for it to open, especially the first time. It's much easier on the system, allows the thermostat to open more consistently and ensures there aren't any steam pockets to shock the heater core.
70 Sportsroof, 427 FE/489 cid, TKO-600, 31 spline 4.10, A/C. modified Mass-flo EFI/reprogrammed A9L/CnC ported Victor.