The '51 is kinda all by itself. It has the mounting pad moved (to accommodate chassis change made for the new for '51 Ford-a-Matic automatic transmissions) but still has the mounting boss for the underfloor clutch linkage used by the "Shoeboxes" ('49-'51), because in 1952, Ford went to "swinging" pedals. They can be made to work by swapping parts, but that's another subject. I have heard that turning the transmission mount end-for end will allow one to be used in the '49-'50 cars but I have never tried it, and doubt it would work.