JimM hit the nail on the head.
look in big truck at your local junk yard. now i am talking high cube, cab overs, what not(not the average 1/2 ton standard truck). basically they share many parts with the chevy trucks(1/2 ton) like the doors and stuff, but sometimes you may find big blocks under the hood, and not the desiel motors. i lifted the hood on a 70 something big truck and staring out at me was a 454 long pump with the Holley double pumper still on it. looked like the truck could still run. most of these trucks are loke car haulers, tow trucks, or flat bed dump trucks.
good luck, Jesse