No shorter aluminum water pump. I put the alum w.p. on my 65 273 (long story) and had to get creative on the pulleys and belts, as have others. I recall posting photos a year or two ago (search). I used a short alum pulley on the water pump, which shares a belt with my pwr steering pump (Federal). The alternator has it own belt further in. The inner-most groove has no belt now. Haven't figured how a Sanden AC compressor will fit. I might share the alternator belt and use that as the tensioner. With the longer pump, I have no room for a fan/clutch and had to use a thin nylon fan from Summit.
