He has a quill stem with a threaded headset. (you youngsters...this is the way they did it in the old days) Everything from the bottom of the barrell on up has a threadless headset now.

Best thing to do is measure the neck and go to your local shop and see fi they have anything. They used to make an extension for that thing at one time. I don't know if they still do.

You could also put a higher rise handlebar on that puppie.