If it hasn't been run in 8yrs, try to have it started before purchasing it. And if it runs, test the shifters, if it has badly hit anything, there will be excessive vibrations. While it's running, check for the water pump functioning - often times the rubber will stick to the pump housing after not being used.
I have an 85 Mariner that had sat for 5 years and it runs great at the moment *touches wood*. If you are mechanically savy and are willing to put the effort in where needed, I'd say go for it. Though, be warned, the older motors have harder parts to find.
