Here’s a parts manual I posted the other day.
There might be two, maybe three P/N’s for crankshafts as ’56 was the year these motors came with either a lip seal or a carbon seal on the lower crank journal. I believe FR mentioned some cranks also had a sleeve on the bottom of the crank which tended to fall off. Regardless, try and go with a carbon seal as they have proven themselves over time and the lip seals tend to fail.
https://www.aomci.org/wp-content/uploads/2022/04/1956-Evinrude-15-hp-Parts-Manual-1.pdf
