So I just picked up an imaculate 2wd 87 long bed and I have a burnt 90 3/4 ton, can I just swap the trans, diff and t case into the 2wd to make it a 4wd pretty easy or is the frame different?

Also if that is too hard can I just swap in an 833 OD trans into the 2wd in place of the 727 ? I have clutch pedal, slave master and a matching bell housing and trans for the hydraulic slave 4 speed.

im fairly sure the front part of the frame on the 4x4 is different ,BUT<you might be able to do enough changing to get the 4x4 front axle to work,but its a lot of looking and comparing,plus drilling out rivits
sounds easier to put the good body on the burnt frame truck

this is a great build, it is a Cummmins, but 2WD to 4WD, but should give you an idea on what is involved.

https://www.dieseltruckresource.com/forums/1st-gen-ram-all-topics-93/crewcab-update-305923/

The 833OD/727 swap on a 2wd chassis is a direct swap if you don't consider you really need the 4wd/4 speed tunnel to have room for the 833. Not counting pedals/bell/etc...

Its a lot of work, I would consider finding a 4wd frame and swapping everything to that.

The 2wd to 4wd conversion varies depending on the truck. I have NOT worked on a 1987 before. I have no idea if there were changes in the frames compared to the older trucks.

On the older models, the 2wd 1/2 ton trucks had a light duty and an optional heavy duty frame. The majority of the 2wd 1/2 ton trucks used the light duty frame. (These heavy duty 2wd 1/2 ton trucks used the heavier gauge frame rails like the 2wd 3/4 tons and 4x4 1/2 tons.) The light duty 2wd frames did NOT typically have the holes to mount the 4x4 cross member. A friend of mine had a 2wd 1/2 ton with the heavy duty frame. His frame had nearly all the holes to mount the 4x4 cross member. He knocked the rivets out and swapped cross members. It was a fair amount of work, but most everything lined up and worked properly. His truck had the small transmission tunnel. His solution was to keep the small tunnel for more interior room and add a body lift on the truck for transmission / transfer case clearance.

Bottom line: Look at the frame on the half ton to see if it has the mounting holes for the 4x4 cross member. If it does the swap MAY be feasible, if you don't mind doing a considerable amount of work. The other option is to swap the nice truck body onto a 4x4 frame.