[dsraven]

thenassembly manual has dimensions for nearly everything and it is available from the tri5 site for free download. possibly download that and print the page with the dimensions you need to ensure the new cab mounts, floor and firewall patching results in a proper fitting set of doors, fenders and hood. it will also show you how many spot welds hold things together and where they will be located. the cab mounts are a sandwich affair at the step and door pillar end and there are a few parts there at the bottom of the pillar to fill the pillar hole and provide strength and also a bracket to attach the lower front fender bolt. when the cab supports and the floor rust out they get weak and the weight of the firewall and front of cab can make the whole unit sag. you may have noticed the floor seemed to drop down at the front below the pedals and that is part of the sag thing. this is why I always recommend to fit the doors in the cab openings and cross bracw stuff before removing the doors to allow work to be done, so the doors will fit when the repairs are finished. the, remove the old mounts and clean up the area to bare metal, getting rid of any metal that is suspect for thickness due to rust. sandblasting can really help here and will quickly show up thin spots. all the parts for the area are available from the patch panels section of the various parts suppliers. when you are ready mock everything up with cleco fasteners and vice grips after you have punched a few holes where you will be spot welding the parts together, or leave that part untill after you have fir the parts and then mark the weld spots, dissassemble and punch the holes at that point. I like to use a piece of square tube or angle iron vice gripped to the ab mounts t connect them side to side and that keeps them flat and level in relation to each other so the floor will be flat and level. if you don't have some cleco's and the cleco pliers they are relatively cheap on ebay or amazon and really help keep things tight together as well as acting like a third or fourth hand. the c clamp vice grips are also invaluable as is a hole punch that will punch a big enough hole for a good spot weld. a step drill can also be your friend here as they don't chew through the metal like a regular drill bit does so they don't leave a piece of steel on the back side of the sheet metal. I usually buff the parts and spray them with some weld through primer so the parts will have some protection between the layers when done, then either clean and epoxy the area or clean and coat the area with weld through primer, which is high in zinc, so it doesn't start to rust before I get to the epoxy stage. the weld through primer actually comes off fairly easily using laquer thinner but will stick good enough for protection untill the time comes to remove it and sand before the epoxy stage.
anyway, long story short, before you weld ensure the doors are gonna fit the cab otherwise you extend your repair time and your frustration level. they need to fit the cab well, then the fender gets adjusted to fit the front of the door, so don't be too concerned with the front fender. if your door is not original to the truck it may not fit that well either as door swapping, for me, has produced various results with doors from 3 different trucks. these trucks were put together by hand mostly and the fitment was just good enough to allow the door to latch, not really worried about the gaps etc.