They actually make fork stem extenders too. I saw some on ebay. They go down into the fork like a goose neck would and cinch like a normal.Now a threadless 1" or 1 1/8" shaft extension is sticking out of your fork tube, then you have to use a modern thread less clamp-on bar stem. I have no experience with them but the concept (if I have it right) was cool.
Good luck!
Good luck!