Congrats, Bob. Sounds like it might have been both the fuse and the ignition switch. My very first advice in my post above was to carefully inspect the fuse, saying it can be deceiving. The reason I said that is I got stung by that more once. In one memorable case I wasted a couple of hours taking the dash half apart to do further investigation to find the fault as the fuse looked perfectly okay when all along it was the ends of the fuse having worn through because I would occasionally spin them back and forth a bit to make sure they had good contact.

There are all kinds of reasons why it might not be idling smoothly, including vacuuum leaks, fouled plugs, old ignition wires and dirty throttle plate. As long as it's reliable and not going through too much oil and gas then for a 40 year old car, I'd cut it some slack and say it's just got a quirky personality.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now