Alright, hold on, what doors are you thinking of swapping, brick ones on an OBS? You can use brick panels on OBS doors no problem, but if you try to run OBS panels on brick doors the vent windows won't open unless you hack off the "horn" at the front top corner of the OBS panel (take a look at both your OBS and your brick, you'll see what I mean). Hanging the entire brick door, panels and all, on the OBS will work, but your OBS dash corners won't visually match the brick panels. Another thing - the OBS door harness bellows are fatter where they enter the door, meaning you'll have to enlarge the opening in the brick door for it to fit properly. If hanging an OBS door on a brick, the opening in the OBS door will need to be downsized - cutting a small area around the brick opening and welding or riveting that over the OBS opening does the trick.
Door handles, both OBS and brick use the same plastic POS. You can replace them w/ metal ones from a slantnose. There are two types to chose from, one is a F0 casting (used on '80 and '81 trucks, possibly some '82s as well) and the other is F2 casting (used on '83-'86 trucks for sure, possibly on '82s as well) - difference is in length, the F0 casting is longer. F2 handles are direct bolt-on affair on both OBS and brick doors. F0s will clear brick panels, but not OBS panels. Additionally, the "tooth" stamped on the handle mechanism for locating the handle so it don't spin if bolt gets a bit loose is wider on the F0 assemblies, meaning when you install the F0 handles on the brick doors the handles will try to twist on you before you tighten the bolts down good - not a big deal, but one to be aware of nevertheless. As far as bolts go, two are available - one takes 8mm socket, the other is 11mm IIRC - both are the same thread and are thus interchangeable, however I suggest using the larger head ones when possible. I run F0 handles and large-head bolts on my brick, it's how these trucks should have come from factory IMHO. For an OBS use the shorter F2 castings and again large-head bolts. Handles can be swapped w/o pulling door panels, however cross-threading the bolts is very easy then so it's quite a bit less annoying to just yank panels for this job.
Seats - reg cab and crew cab seats interchange, ext cab are their own special breed. If you want air ride in a reg cab or a crew, you should be looking at cabover trucks because some of them have shallow-mount air seats. The typical big truck air seats have frames that are quite tall, may work in a flat-floored ext cab but not in a reg cab or a crew. Another option would be the spring-loaded frames from an import truck, the J70-series Land Cruiser ones are actually very nice and sturdy but good luck finding them as those trucks were never sold in the US (ah, if only). Not sure if normal US models (60 and 80 series) Land Cruisers would have those seats. Custom work is required either way.
Windshields should interchange between brick and OBS, however I recall something about the slant-nose one being same shape but thicker. Which IMHO would be an advantage. Door glass is identical between bricks and OBS, but does not interchange w/ slantnose unless you use slantnose vent window frames as well. Don't remember which was the wider one.
