Here’s a diagram with original P/N’s for a ’51 Johnson RD 25 horse but I’m not sure though if Johnson and Evinrude were sharing parts on these motors back then.
The base gasket is #302625 with an adaptor gasket under that of #302821. The impeller #778891 if you don’t want a Sierra. I believe the quad seals to replace the o-rings in the carbon holders is #305098? Someone correct me on that if I’m wrong, please. The quad seal is a better choice when replacing that o-ring. IMHO.