are the frames different? what auto trannies came in the 3/4 ton trucks? what rear ends? specifically the 81-87 models. motor options? my main question is the difference in the frames...what different about them if anything. thanks
greg

The frames are the same. You'll have the same tranny if it's a standard, but most likely a different transmission. The 1/2 ton will likely have a 350 or 700R4, while the 3/4 ton may have a 350, 400 or 700r4. The 1/2 ton may have a 6 cylinder, 305 or 350, while the 3/4 gets the same engines, with the option of a 454. In the 1/2 ton, you'll have a 10 bolt. The 3/4 will have a 14 bolt, either semi floating or full floating. Most everything depends on the gvw of the 3/4, to determine which heavy duty parts it will get.

The frames are not the same.

tigweld, what's different between the frames? i have a 1/2 ton with the 350 and soon to be a 700r4 and soon to be 12 bolt.

I know a gooseneck trailer may sound funny being towed behind a 1/2 ton, but I am going to start building a trailer for my Nissan. Goosenecks tow a lot better and when I build it, it won't weigh a whole lot more than a standard bumper pull. I am thinking about just boxing the whole rear section of my frame, building a gooseneck hitch out of 2x4x1/4" rectangle tubing bolted down with 6 3/4" bolts(3 each frame rail), and a set of leveling airbags for towing. The trailer will probably weigh no more than 6500-7000 lbs. MAX. My truck is going to have 3/4 ton front coil springs, a 12 bolt (keeping the 5 lug pattern), 3.73(or 3.90) gears, the 700r4 built with all B&M parts and about 480 hp. I towed my Nissan on a bumper pull trailer loaded about 6000-6200 lbs or so and it did ok, a bit soft in the rear and the load was really even. It was tough taking off on hills with my turbo 350, and 3.23 gears. The motor now has appro. 300+ hp. I guess my main concern is will it handle a gooseneck trailer after boxing the frame and building a stout crossmember and section for the gooseneck hitch? I just want it because it tows so much better. Thanks.
Greg