Greetings, Dallas-Welcome to The 'Bolt.
I'm not totally sure if GMC's were the same as Chevy's of this era, but you could get a floor shifted four speed (SM420) in the Chevy's. You might wish to check out Old Car Kook's website
www.oldgmctrucks.com for more GMC specific information. He has an interesting site, LOTS of info!
Best of luck with your project. If you've got more questions be sure to post 'em-someone here will have an answer!
Regards,
Wannabe
