Short snout water pump?

Second. The cast iron water pump (1964 - 1969?) is about 1" shorter. The inlet (lower hose) is on the passenger side and is 1.5"D instead of the 1.75"D of the later aluminum water pump. You would need a different radiator and the early A SB radiators are harder to find.

You will have to re-position your accessories and maybe get creative with pulleys. If you have a later harmonic balancer, it might be thicker so your crank pulley slots may be off. If you have power steering, I think you must change to the earlier TRW pump and brackets, or maybe add 1" spacers for your brackets.

What are you doing to open this can of worms? You should get a fan to fit most setups, but maybe not a fan clutch.