[5th TA]

Not saying the cam couldn’t be worn, but if it ran decent going out and terrible coming back, not likely things changed that quickly with the cam condition. You could start with pulling plug wires one at a time from the distributor side while the engine is running. If pulling a plug wire doesn’t have an effect, you have a dead cylinder. On the other hand if you have an RPM drop then that cylinder is producing power. Pull the plugs on any dead cylinders and check the condition. You could also do a compression test on all cylinders. Any recent changes with fuel or fuel fill up before engine started running poorly? Large vacuum leaks or carb loosely mounted to intake?

Be careful when pulling plug wires if you have never done this before, you could get a shock. They make insulated pliers for this if you want to play it safe.