Yes, outboardnut2, I do have cover, faceplate, lower pan parts from the 15 HP Johnson and hopefully they will fit.
Yes, but the head mounts are different. The Johnson hood has bumpers in the back, the Evinrude bumpers are on the side. In later years, the 18HP heads might have had a common head casting with mounts for both brands. The forward starter mount brackets are probably different as well, but you could use the brackets from the 1956 15hp, on the 18hp block.
Please don’t try to swap the cylinder heads though, the two engines have different bore sizes
