Hellfish,
I am not if all post-1948 crankshaft pulleys are like the ones that I have worked with, but the attached image (at least I hope that it is attached; this is the first time that I've tried to include an image) shows the 3/4" square (approximately) hole in the pulley. a 1/2' to 3/4' adapter fits well, and I have never had it slip.
Hoyt
[img]http://static.flickr.com/34/70742224_8401afa981.jpg?v=0[/img]
