Re: rebuild?
In my opinion, if you are going to do the work yourself AND the block is in good enough condition to rebuild, there is NO question: Rebuild it.
However, if you are going to have someone do it for you, many times the economics are just not there: For example, I charge 450 for disassembly and assembly plus parts. Now, A piston is about 125 and boring a cylinder costs around 60 bucks here. Then add in gaskets and incidentals and you are up to at least 700 bucks. HOWEVER, try buying a good running 85 for that price--not so easy. And, If you do rebuild, you now have a known engine.
The engine is dirt simple and almost no special tools are required. If you have 8 regular fingers and 2 thumbs, you can do the work with the help and advice you will get here