Okay,How about a 1953 Evinrude powerhead on the 53 RD.The base gasket is the same,so the water passages must match.All the individual part numbers are the same,BUT the part numbers for the block and crankcase assemblies are different.Why?
The only differences between Johnson and Evinrude 25’s of the same years are the cowling and the parts to mount the cowlings. I don’t have the slightest idea why the cylinder & crankcase numbers would be different, but I’ll look into it & see what I can find. Stay tuned.