I vaguely recall that question coming up and the answer being that the Saginaw was never used on the iron w.p. I changed to the later alum w.p. in my 65 273 and had to buy both a Federal p.s. pump and brackets for it (Bouchillon, I recall). A Saginaw setup might have been a better choice (more efficient and common I read). I don't suggest you follow, since the 1" thicker w.p. caused numerous other problems (pulley alignment, ...). Any reason you can't use the original TRW pump? Rebuild kits are cheap. I rebuilt mine before I found I couldn't mount it to the alum w.p. (can use it on my 65 Newport). If you change to Saginaw or Federal, you will need different p.s. hoses, plus the mating fittings on your p.s. gearbox. I did.
Are you sure you can't adapt it to work? As I recall, besides being ~1" thinner, the only other main difference of the cast-iron water pump is that it has a little triangle sticking out with a hole that the TRW p.s. pump bracket uses. If that triangle doesn't interfere, perhaps all you need is 1" spacers (Ace Hardware has purty chrome ones) to attach the Saginaw p.s. bracket. If it does bump, cut off the triangle.
