not speedy...
I drove 2 seventies vintage GMC C-6500's we had at the junkyard,one was a "box" truck,the other had a flatbed...both had 366 motors,not sure what gears they had,probably 6.17's or something close..they had govenors on them,and 60-65 mph was "flat out" top speed..more like 50-55 uphill though,loaded...
You could coax them up to 70 mph down a hill,but the engines were winding pretty high..but they could carry anything you could pile in the back without a problem..they didn't accelerate very quick though...the flatbed one was easier to drive,only had a 18' bed..the box truck was a 24 footer,was very difficult to turn around in tight places..
The box truck had a 5 speed with a 3 speed auxilary tranny,that I never tried using,all it did was make it crawl slower!.. the other truck had a 5 speed and a 2 speed rear end..I never did get the hang of shifting the axle right..always sounded like gears grinding to death every time I shifted it!..my co-worker could shift it without a whimper though!..

..I'd say such a truck would be OK for what you want to use it for,for shorter trips,not the hot setup for a cross country jaunt ,IMO..
