Personal opinion! That is an old, inefficient 2 stroke. Now sure how much you plan to run it, but here are some random thoughts.
1. A modern 4-stroke will cut your fuel consumption by 50% or more for the same amount of usage.
2. When on the water, you want to have extreme confidence that your engine will get you where you want to go, and back to your home port. Even if you rebuild that Mariner, will you ever have that level of confidence?
3. The best thing you can do for any outboard engine is to run them often and run them hard. If that is not in the cards for you, then you are far better off with a 4-stroke engine rather than a two-stroke engine. The four strokes can handle a lack of use better, assuming they are meticulously maintained.
4. On the other hand, basically, a 2-stroke engine is simpler and easier to maintain, and there are fewer things that can go wrong. But again, frequent usage is key to keeping it running in good order.
5. Never buy a used marine engine unless you are a highly trained mechanic, or your BFF is one.