Thank you Dennis.
I remember back in high school auto shop class we had one of those little spark plug cleaners that sandblasted those puppies clean. The kids in my class all had a good time cleaning up their dirty spark plugs and making their cars (or their parent's cars if they didn't have one of their own) run a little better.
I thought a bit about what they may have rebuilt/reconditioned and sold back in the day that you can't really get now and spark plugs seemed to fit, and all of the GTOs most certainly had that part in common.
Buying a set of cleaned-up and tested spark plugs may seem bit far-fetched for those of us who really who really think nothing of buying a new set of plugs and tossing out the old ones. I figured buying a bargain-priced set of reconditioned spark plugs back in the sixties when it was not uncommon for folks to tune up the family car in the driveway wouldn't be out of the question for any budget-minded car owner.