if you really meant "threaded headset" you will find that most steerer tubes were cut to within one or two millimeters of optimal length. there is little to play with on them. it was the nature of the beast. height adjustment was usually accomplished via the stem hosel. although i once was testing out a slightly too long threaded one inch fork and had to add something to add a little space. once fitted it worked fine that way while i was testing it.