Very nice and short shafts no less!!! They really aren't that hard to work on. Lots of helpon here and parts aren't that hard to find. You can look up any part numbers on marineengine.com and either buy them on there or see if Amazon has them. I've used my '59 Fat Fifty and my current '67 80 hp on brackish water for years. I alwasy run fresh water through them for at least 10 minutes to flush and still running fine. There is a product called "salt away" to help with the process. I'm going to switch to unsing that.
The Lark looks like it is all there and not bent up. Those are really iconic looking engines when painted. They are excellent runners as well. That one you have is also much quieter than the other style. They are a pleasure to run.
The '69 40hp is another one that is a great runner and will have noticeably more bottom end than the Lark will. Both easy to work on and keep running.
The 1958 will require a 24;1 mixture and the 1969 will be okay with a 50:1 mix although I always recomment a bit richer.