Since you don't know the history, and it doesn't run well enough to tune, your best path is to verify that the various rotating parts are timed correctly. Hatepotholez is going through the same situation and just found that his damper pulley might have slipped, for example.
I would start with the ignition timing mark on the damper pulley at zero and verify that the cam shaft is in the proper orientation, the rotor in the distributor is pointing at the correct electrode, and the plug wires are properly placed. 1-5-3-6-2-4, counterclockwise, like site's picture. Then rotate the engine by hand and check valve lash, correcting any that are off. The older engines are known for worn valve seats due to unleaded fuel. That could cause some backfires, or popping back through the intake (some people call that front-fire, I think). They're also known for throwing lash pads, which would cause the valve not to open fully.
Anyway, you've spent enough time on it to justify starting from zero. Set all of those things once, and you won't have to wonder about them.