The 70/75 is derived from a 90 horsepower block with the three carbs removed and a single carb and manifold added. Even though it only uses a 10 inch prop, it does give surprising performance. As with all Force engines dealers simply do not want to work on them but parts are available. Tilt/trim parts are another story though. They are getting difficult to find. but again, if you are persistent you can usually find what you need.
As for reliability, they are no more nor no less reliable than the other major brands. Keep TWC-3 oil in the fuel at 50-1 ratio and it may very well run for your grandchildren.
Before buying do a compression test to be certain all three cylinders are high and equal. Remember EVERY engine sold was "Running when I put it away"
Be certain the all controls, cables, and wiring comes with the engine.