I think I would be careful about the stuff I put in the oil on these old engines. If it has an oil filter it may be a bypass filter rather than a full flow filter.

If something turns loose and the oil pump picks it up it could go to the bearings rather than through the filter. The screen mesh in the oil pump pickup tube is small, but still large enough to let some stuff through that could eat up bearings in a heart beat.

I like Sea Foam, I just think I would be careful about using it in the oil.