It looks like you've got a Mr. Gasket #7667 pickup shifter. (Link) If so, the shift lever bolts on and you can make one out of some steel rod to fit your cab and seat. Here's a link to the install instructions. Another option is Patrick Dykes ((520) 836-1117) shifter for the Saginaw 4 speed. It enters the cab at the same location as the factory SM-420 trans stick does. You could use it with a 3-speed by locking out the reverse lever.

regards,
Leon