I used the Summit aluminium pulleys on both my small and big blocks. Perfect fit and belt alignment, haven’t tossed a belt yet. I can dig up the numbers if you’re interested. My initial install in my Nova was single groove water pump and crank on the small block. When I moved the motor to my Beaumont the crank was changed to a two groove. Have a big block in the Nova now with a single groove on the water pump and a double on the crank. The swaps leave me with a single groove crank pulley sitting on the shelf.