Re: oil mix ratio
The '63 is 24:1 and the '66 and '72 are 50:1 I dunno about Mercs. Heck if it is more convenient, run all the Evinrudes and Johnsons on 24:1. It won't hurt a thing. But it probably isn't wise to run the early ones on 50:1
There was a time that Merc claimed their motors were so precision that they needed plenty of oil and they resisted going to 50:1. Ever hear of hogwash?