From the factory, for the 1977 GMC Astro/95, GMC offered the DD 6-71N, 8V-71N, 6V-92, 8V-92, 12V-71N; Cummins NTC290, & KT450; and the Caterpillar 3406. Now, this isn't to say that someone didn't have the Cummins NTTC475 & stuck it in a glider, or repowered an older Astro (the kit is basically a 1972-76, give or take a little).