Rear wheel drive
My friend has one of these cars and he says when the engine is revved too high, it starts to backfire and and "chug" along.

It sounds to me like an ignition timing problem, possibly. I at least want to eliminate that as a possibility. I have a timing light but what I do not know is where to find the timing window in the trans or wherever.

So what degree BTC should it be adjusted to and at what RPM'*? Idle?
And where would I find the window?

I can't speak specifically for that particular engine, but the older engines generally had a line indented in the harmonic balancer for the timing mark. Then, there would be a tab attached to the front of the engine that bent over the balancer that had the different timing marks on it. It is usually on the driver'* side of the car. As for the timing and speed, I no longer have any servicing information that old, but if no one speaks up, you may want to check at the library and see what they have.

Also..if that'* a distributor engine as I think it may be..check for corrosion on the modules inside the distributor. They can drag down the voltage and cause quite the issues as well.

I had an 84 Cutlass, same engine. always ran fair, idle always lumpy though, found the timing chain really loose. Once we changed that, it smoothed out pretty good. I think it had 140k when that was discovered.

Worth a shot if the easy (cheap) stuff doesnt help.