Originally Posted by
jimc101
Before you even get into the can it be done safely issue, do you have a frame and fork that are the same spec size wise?
Generally, threaded = 1" & threadless are either 1 1/8th" or tapered, there was a crossover back in the late 90's where some bikes had 1 1/8th" threaded, but this was uncommon, and doesn't really match your vintage description.
Your question is a good one but there were, and still are, 1" threadless forks available. Nashbar, for one, still lists them. Also, I had a '92 Trek 7000 MTB with a 1-1/8" threaded steerer so they were available in the early '90's too.
All that said, threading a threadless steerer, no matter what it's diameter, is a lousy idea.