A couple of possibilities to check,
1. Spark plug leads, particularly coil to distributor, but if the car is missing it may be down on one spark plug lead. Not uncommon that the issue will only show up under load. You mentioned one spark plug was fouled, this may be because that spark plug lead is shot.
2. Fuel pump, might deliver enough fuel to idle and rev with no load but not under load. If mechanical the diaphragm may be shot.
When you have issues like this always change one thing at a time, check to see if the issue is rectified then move onto the next. Don't make 6 changes then test. For one you wont know what the problem was, and secondly you may end up chasing your tail.