Thanks, all. My goal is to spend as little as possible. As you might be able to glean from the picture, this is an old steel MTB. The decal on the frame claims that it's chrome-moly, but the fork has a "Hi-Ten" decal, so I wanted to upgrade the fork to something else. The yellow fork is a Tange chrome-moly fork from the 1980s. I knew it would be too long, but I also want to set this bike up as more of a touring bike with upright geometry, so the length of the fork is fine (with spacers). Until I'm confident of the setup, though, I do want to keep my cash outlay small. I will likely see if I can source a centering nylon washer locally for the 1" steerer and might sand the threads out of the cone with some sandpaper wrapped around a tapered dowel. That should keep it more or less of a circular hole, and the nylon washer should lock in pretty good I'd think.

I probably will either cut the steerer or have my bike shop do it, as I really won't need the threaded portion.

I have only two bikes in the family with threadless setups, and they're our daughter's bikes (which I try not to mess with!), so I don't have a lot of experience with threadless (which is why I want to do this conversion and learn more about it and gain experience with it).