I have for sale a double pulley for the short water pump small blocks. The outside diameter is about 6 5/8". I've looked it up in numerous books and basically it seems to fit all the 283 307 327 and 350's from 64 until they went to the long water pump (which was 1969 on most cars except for Corvette, 1973 on pickups I believe). The double bottom pulley is needed for air conditioning applications. The power steering pump is run by a separate pulley which would piggyback this pulley. Once the power steering pump pulley is added, the "top" or outer groove on this pulley would become the center pulley which is what drives the A/C compressor.  Making sense I hope!

Anyway, I'd like to get $20 plus shipping for this pulley.

I also have the identical thing for sale in a separate listing except it's about 7 1/4" diameter, part # 3850838. The parts books are really weird, it's hard to determine exactly which of the two pulleys is correct for a specific vehicle because a number of times the numbers seem to overlap.