the C65 has a 366 long block. it gets around 6-8 empty and 6 with a heavy load. the more time spent in the low range gears the worse the milage is.
Thanks for the info. That's about what I figured on the mpg. I'm looking at an '87 this weekend. It has a 366 and Allison in it. I'll have to see what it feels like with the auto trans. I have another one to look at as well. Its an ex-firetruck converted to dump. Less than 10,000 original miles and literally looks new. The guy says it has a 350 in it, so we'll see if he really knows what he has. It's pretty flat around here...but not small block flat.