3/4 GMC to 1 ton

[Angelo]

I have a 1971 GMC 3/4 truck that i want to make it into a dually and take the 350 motor and 4 speed tranny out and replace it with a 6.5 turbo diesel and automatic transmission. The parts truck that i have been going to see are 1 ton duallys from 92 to 2000. The question is are the 1 ton cab and chassis dually is the same as a 1ton dually?? Reason i asked is because i see the cab and chassis differental looks shorter than a regular dually or is it just my eyes lol. I am going to be adding the step side fenders on the long bed..