Im looking at one for a vintage restoration. Price is cheap $100.00 with controls,Its a 63 johnson electromatic, owner says it runs,works, I really need the short shaft model at 15", this one has the long shaft 20". I notice the only difference from the outside is a 5 inch spacer on top of the lower unit. Is this unit removable to make it a 15? Im still going to ppurchace this if only for parts, also is the cowling interchangeable between the evinrude and johnson? Last are most of these years interchangabe between the years.