1st pic is measurement from TOP of the cam drive pin hole to top of taper. 1.515 same on both crankshafts.
The top crankshaft was removed forcefully from a 53/54 Evinrude 25HP. cast into the top counterweight is 302??. Probably 302530. Etched into the flywheel taper of the NOS is a boxed M and number 203655. I’m thinking that the original castings differ between these crankshafts, maybe because of the supplier and so the machining drawings differed and so the crankshaft numbers differed but that the interfaces are the same and both crankshafts are completely interchangeable.
I did not find significant dimensional differences between the crankshafts in the top bearing/seal area. Maybe more experienced people could spot something. Only thing I noticed is the transition between the cam drive pin surface and the bearing surface where the seal rides is more gradual on the 203655 crankshaft. That would make the carbon seal easier to install on the NOS crankshaft but the 302530 crankshaft had a carbon seal on both ends when I removed it from the motor.
WRT the flywheel not seating maybe this would help. Last year I was unable to get the carbon seal onto its surface on the bottom of a big twin crankshaft. I just could not force it into place despite lube, etc and expected that I would soon break the carbon. Inside the carbon I had put a square ring instead of the originally provided o-ring. In the end I had to put a new o-ring in and the seal then slid into place with some difficulty. I don’t know why the seal would not go up with the square ring. I usually replace the o-ring with a square ring as recommended by the experienced people on the site. But somehow there was no way that seal would go into place with the square ring installed.
