A while back, I purchased a 1980 F100 with a 300 engine and a C6 trans. Other than being a bit rough, it had 3 major problems. A starter going out, a running problem, and a previous owner who unfortunately had owned a toolbox.

Starter problem. It was eating the starter drive. Autozone application called for #3153 which is what the previous owner had put in. Would eat the edge of the gear off even after installing a new flywheel. Application from year before called for #3124. Never got one to work quite right, starter drive sometimes would engage and would drag badly when hot. (cable bolt was only an inch from exhaust pipe.)
I fixed this by taking a new early model(aka3124) starter drive and putting it in the 3153 case. So far this has worked fine.

Running problem. Motor would sometimes be hard to start, run rough or shut down for no reason. This ended up being a combination of a worn ignition switch and a erratic control module. Replaced both and truck has ran fine since.

Previous owner had done quite a bit of motor work to this truck including a new cylinder head. Unfortunately he didn't realise there was a reason to have a PVC valve and blocked the system off. Took me a month after I got it to get the rings to reseat. 300's are tough motors though, rings reseated and truck runs great.