Thank you all for your suggestions and comments. I've decided to go with a 2-stroke 8hp Nissan outboard, with the 12v charging option. At 60lbs, even my tired back should hold up to its weight. I'll let you know how it works out.
Thanks again!
BTW, the 2-stroke is smaller than the 4-stroke, and should fit in the well without a problem. I'll confirm that in a couple weeks, or let you ridicule me for not following commanderpete's advice.