[yossarian19]

Yes, I think the 5 speed is a NV3500. It's good to around 300 ft-lbs. Not much else to say about it except that it's a PITA to rebuild one, from what I've read.
The big advantage of a NV3500 vs a M2x 4-speed is the overdrive, of course.
Without overdrive the 4.8 won't be making enough torque to get any performance *and* run 70+ mph at a cruising RPM. You'd have to pick one. I wouldn't want to run the 4.8 without overdrive and steeper gears in back, it would be kind of a let-down in a hobby truck.
I have a 2003 4.8 + 4L60e and 4.11 gears in back of my '57 longbed. It's fun and the overdrive lets it loaf on the highway. When it drops to third it takes off and makes you smile.