Well done that man. Isn't it curious and infuriating when you find that a part you thought was good turns out to be faulty.
I once in my late teens had a Mk2 Cortina, and replaced the distributor cap and leads, to cure a misfire. It did, so I put the old cap and leads at the back of the shed. A neighbour's daughter came back from college with someone in a Mk1 GT estate. Apparently it had failed at some point, and been retrieved to a shed. We were asked to help, with little success. Mum had put Sunday dinner on the table, so we went back home, after giving the owner this old cap and leads, with the warning that it had caused issues on mine.
We're sat enjoying Mum's cooking, when this green blur flashes past our window at high speed! Seems it worked just fine on his!
Interestingly, Ford had two different distributor caps for those engines, looked and fitted identical, but the fixing clips were rotated quite a way. Threw the timing a mile out.