OK, If your friend is wanting to build a car hauler, here is the best advice I can offer. I have a 1939 Chevy COE 1 ton hot rod. Still all one ton, but up-graded. First, yes he will need to tell the glass provider weather he is going stock or going electric. The glass will be sized different. Only the doors will be different. The windshield can be changed to a one piece glass if he doesn't want to keep the crank.out windshields.
But if he is building something to drive every day & make a hauler, the best way will be to go find a complete 1 or 2 ton GM stepvan for a Donner, like a bread truck or moving van, one he can drive & be sure it is road ready. If GMC was made by GM you will find that his frame is a P30 frame. GM still uses the P30 frame rails on big trucks. It doesn't matter if the Donner is longer than he needs, the rails can be shortened out back. He can sit his cab & pedestal right on a newer frame & everything will bolt right up. Use the Donner's gauge panel in his dash, wire it up & drive away with a newer independent front suspension with disc brakes, a V8 & complete drive train that matches. He will save money time & headaches trying to figure what will work together best. When it comes time to replace parts, he won't have aftermarket mix match parts to look for.
I wish I had gotten a complete driver Donner. I found a 1980 Chevy stepvan frame & front-end to started my build. First thing I found was that if I had wanted my truck to sit stock on the frame, all I would had needed was to keep the pedestal on my cab & sit it on the Donner frane, some of the bolt holes in the frame were even in the right place.
My truck was originally a short 107" wheel base tow truck. It's still a short 1 ton tow truck but with no boom yet. I wanted it to sit just off the ground. So I did away with the 10" pedestal & built a tilt cab sub frame. I added air ride all around, 4 bags in the rear to haul the weight. It still has dully wheels & sits 2" off the ground. Because of all my changes I'm still working out bugs but it will work in the end.
Find a complete driver Donner truck...... I once spoke with a old COE builder that builds trucks for a living. He uses Isuzu NPA trucks as Donner's & say's they work good?

Attachments
MYTRUCK.jpg (67.81 KB, 55 downloads)

Last edited by OLDSCHOOL CHEV; 12/28/2019 8:21 PM.

Darrell, W.L.
1939 Chevy COE tow truck/My Stubbed toe
1939 Chevy 2 door Sedan

Car chat means talks about Chevy's. All other car makers only build transportation.
I don't work on my cars, I entertain my self in my garage, so my nabor tells me.