You can go with a Holley projection intake. (52mm) I have a new one for sale. (non-Vortec iron head version) Shameless plug.
Indmar changes the adaptor plate, to use the 50mm TBI, on a stock manifold. (Which looks like a carburator manifold, with an adaptor plate. Not a 100% sure.)
Mastercraft 205, Chevy 5.7 TBI. FOR SALE