I had a 6V53 with twin turbos in a 1961 1 ton ford truck, it actually fit well enough but it was real tight. It had a 10 speed OD Roadranger and worked very well, had enough gears and with 3.73 axle and 38" tires would get down the road too. I put large hydraulic disc brake axles from a topkick and a Freightliner in it, plenty of braking ability. The 1 ton frame was the weak link in the truck, it really should have been built on a larger truck to start with but that was before my time.
For our old GM trucks I'd say 3 ton or larger might be OK to fit a 6V53. Ideally in a truck that had a V engine as an option if not already.
If going through the trouble of fitting a 6V53 skip that and go straight for a 6V53T, plenty more HP and better mileage.
