[D13]

My 87 C6500 (GMC) uses the same doors, windshield, and dash pad as my 87 R10 Chevy.
My GVW is under 26K so no CDL required. 4 wheel disc brakes with hydroboost.
Dual axles and air brakes are options, as is a crew cab.
My rear window is smaller - same stampuing as a pickup but different hole cut out.
Cabs mount different - floor and firewall are different - depending upon which front (mine is short tilt) the lower front of the cab may be different (fenders behind the wheel are part of the cab, the rest of the fenders and hood are 1 piece SMC). Notice the different hood/fender between the last one on the first post and the first one on the next post.
4wd is an option but uncommon, C65's often have dual axles in back, have sen them with tag (lift axle) options.
Many differnet engines and trans', usually 5 speed with or without 2 speed rear, Allison auto optional, 350 SBC, 366/427 tall BBC, 8.2 Detroit, Cat diesels, and I'm sure there are others. Be aware that parking brakes are usually on the prop shaft. Seat mounts are different too. My 87 has the 70's style dash with manual choke, old style column and wheel, wipers on the dash.