Just a few things off the top of my head...
Besides having an A&P do a normal prebuy including compression measurements on the engine...
1) Make sure there is lots of documentation from the build, like photos, color chips/names, serial numbers for all the goodies etc.
2) Make sure all the required paperwork is there including flight limitations.
3) Look under the panel a lot. This is made easier by removing the front seat upholstery and seat back. That only takes a couple of minutes. Take a flashlight, stretch out with your legs in the back and your shoulders on the front floor, and look at everything very carefully. You'll be able to tell a lot about the electrical system by the care that went into the wiring under the panel. Take a look in the gear towers to see if wires, tubing, coax etc. are neat and protected from chafing.
4) Check the log books to see what entries have been made. If the plane is a few years old you'll be able to tell a lot about how the plane was maintained and how good the owner was in documenting things like modifications, improvements etc.
5) Have someone who knows -8s go through documentation and the plane with you. They'll know about maintenance items like torquing the landing gear bolts.
I'll post more as I think of things.
John
