There was only one minor problem: when I went to the parts store to buy the plugs, they didn't have them in single packs; they only had them in 4-packs. (And I have no idea where the hell I got them, either. Probably K-mart, because back then the local K-mart had a really good automotive section and there were no conveniently-located parts stores.) And so, for my Thunderbird's V6 engine, I bought eight spark plugs.
I have pictures, somewhere, of me changing those plugs; in order to change the passenger-side plugs I had to kneel on the engine and reach straight down the passenger side of the engine to get at them. I did them first; and the driver's side plugs were easy-peasy. I gapped them and set them on a table next to the car and got everything ready before starting.
But I had two plugs left over; I chucked them into the junk drawer and forgot about them.
Fast-forward 13 years.
Mom was cleaning out the kitchen, so the cabinets could be torn out, and found the spark plugs. I claimed them--immediately recognizing them as the leftover plugs from 1995--and set them on my desk, where they again languished for a couple of weeks.
Only just now did I remember I wanted to cross-reference the things with my current vehicle, and--sure enough!--the Escort can use them. And since my current '95 burns oil in one cylinder, I occasionally have to swap the #4 plug.
"Better hang on to that; it could come in handy some day." You just never know.
