Early small blocks up to about 69 used the short legged water pump. Most 2 piece or cast timing covers need a long water pump for clearance. I just used a chrome steel one on my currant 355 engine project for the '69 truck and had to grind off a little of the lip on the stamped cover on the back of the water pump to get it to fit. The reason I stayed with the short pump was that all of the other pullys and p/s and alt mounts that came with this basketcase project were for a short pump.

Tom