Stove: Hello and Welcome to the site. If you have a GMC it will have a 228 or 248 Jimmy in it unless someone has changed it out for a Chevy. They are longer engines and are heavy duty as compared to a 216 Chevrolet. I recommend
www.OldGMCtrucks.com for the info you require.
But don't go away and be sure to post some pictures of your ride.