[franken]

Some good suggestions above, but a basic tuneup is pretty much where to start, possibly after the compression check to verify engine health.

Stock plug wires are prone to failure, and not firing a cylinder is a big power robber. Correct spark advance. and ignition are also important.

77 would have a cat OEM and a dual exhaust probably eliminated that. Chances are a change to different mufflers won't make much performance difference.

Go fast parts are in reality secondary to glaring needs bits below...

Unfortunately, old cars are a bit expensive as far as needing initial work goes. They typically need a complete fluid change (engine, trans, diffs, brake, coolant), which costs more than people think. Brakes, front end wear parts are normally worn as well. Wiring is typically trashed, and I normally on a new old vehicle have to put in a new battery box, PS pump, box and hoses.

That's a few thousand to pay someone for the work and maybe half for parts.