If you are handy and careful, you can make an adapter out of a spark plug. Weld a plate over the end of the spark plug shell that you gutted, and drill and tap it for the glow plug. You have to be careful not to mess up the spark plug shell threads, and you have to check for piston clearance to the glow plug when you're done. The plate will need to be recessed into the spark plug shell; not just welded over the end.

Good luck, and can't wait to hear your results,
AV8TOR