The bolt spacing is different. There is one bolt moved over on a forged crank pulley. You know how the bolt holes only line up one way? Then you,have to rotate the pulley to get all 6 to line up? Ever had that happen?
Then the early 70's they bolt on without any specific orientation because the bolt holes are spaced evenly? [b]Somebody sells a crank pulley with an oblonghole to fit both balancers. Does this sound familiar yet?
I'll try to get a photo.
WOW, file the hole, just like I said in my first post. Somebody sells that. I'm not chasing anything, I put up pictures to show the difference.