Re: 58 and 61 larks
No, I don't believe they are similar in most respects.
The 1958 is the older design and is basically a 35hp Bigtwin painted in gray, with a "fancier" hood. The 1961 Lark III is of the "Super Quiet" design and is a 40hp motor. This motor has a different lower unit, water pump (dual tube), midsection, lower & upper cowl, fuel pump (it has one and the '58 doesn't), fuel tank, and powerhead. I don't believe that it has the air silencer on the front of the carb and the carb will be somewhat different. The Lark III probably doesn't have the compression release mechanism (for easier manual starting), that is found on the earlier Evinrude, either.
There will be a few parts that will work on either engine. Off the top of my head, I would say those parts would be the available props, starter, generator, recoil start assembly, points/condensors/coils, and vacuum cutout switch. There may be a few more that I am forgetting.