Halo mfg has material for 40, M2/M3 browning plates, these plates are correct in every aspect and are the best .50 plate available. He is willing to do a run of at least 20 pieces at a deep discount. These can be 80% or registered plates. he also will do the original colt engraving on them. these normally sell for $475.00 for a basic plate, if he gets over 20 comitments the price will drop at least $100.00.
Even if you don't want to build one right now it is a good investment, specially if you get a registered one and they do a .50 ban.