That's a later 261, at least a '58 judging by the oil filter and lines. They pulley you have is for a 216. Check the salvage yards, should be able to find a correct pulley for it. If you don't have one, you may want to grab the fan, too. I would suggest looking at school busses, the later ones have a 5 blade fan that is much better than the 4 blade. You'll want to consider adding a shroud, too, for best efficiency.
