1983 Plymouth Scamp GT - Lacking in Performance

Good tip on the O2 sensor wires!
Other things to look at should be: What was the code set with the Check Engine Light? That's the 1st place to start.
Next, the carbs had a rubber insulator plate that mounted the carb to the intake & they used to crack & cause vacuum leaks that would cause hard starting cold & lean conditions when warmed up. Spray carb cleaner around the base of the carb with it running(air cleaner on if possible) & listen for the engine to change speed.
Another thing is the possibility of the catalytic converter is clogged or partially blocked up & gets worse as it heats up. Check by hooking up a vacuum gauge to manifold vacuum & bring the enine speed up- if it continues to drop or is considerably low, possible catalytic converter failure. Also check for excessive back pressure. Many ways to do this, but the easiest quick check is to bring the engine speed up & see if there is a good amount of exhaust coming from the tail pipe. You can do this while doing the vacuum test if you have a helper.
What condition is the timing belt in? Has it been replaced in the last 60,000 miles? It's possible it may have jumped a tooth or so. That would definitely cause loss of power.
How is the ignition? Is it misfiring? What do your plugs look like? Plugs can tell a whole lot of the story on how it's running.
I hope I didn't throw too much at you all at once. Just some ideas of where to look.
I hope this helps. Good Luck!