Ok due to request of a few members, here is some cab corner replacement and body work tech by me, on the 1984 c10 owned by my dad. Big swims350 LOL. I will also throw in some pis of my 88 since I had some in progress pics and a little more detailed then when I did his. So if you are wondering the red/black is the 88 k1500 and the blue and then white is the 84. Here's what you normally start with.. As you can see I removed the bed, it gives you better access and more work space. Also alot of the times the rust will wrap around the backside. Now to remove your bed, that's a job in itself and probably another tech, but I'll tell you about it now, don't have pics though sorry. The beds on the square bodies have carriage bolts, round head inside the bed, visible in the bed floor, square section under it and a square spot made in the bed to hold it. These often rot out or get soft and spin. I suggest 2 people for this job. One to stand on the head of the bolt, then you underneath or your helper, soak them good with your choice of penetrating oil, I hear a 50/50 mix of acetone and atf works better then any store bought but have never tried it. Ok I use a 1/2 drive impact and it was a 3/4 socket pretty sure, yours may be different. there are 8 of them, 2 in the very back at the end, 2 about a foot forward of the furthest back 2 and then in the front 2 at the very front, and 2 a foot back from them. You will most likely need a swivel as well. Now if the bolts spin still you can spot weld the head to the bed floor, or cut a slot in the head, or cut off each side so you can get a wrench on it. When you get that done the taillights unplug from the frame side and they stay with the bed, there's a ground wire too for them that comes loose, and a ground strap on the gas filler neck that bolts to the bed. You also need to remove the screws that hold the filler neck to the bedside then move it out of your way. They have 3 torx heads to hold the plastic to the bed and 3 7 or 8mm head bolts to hold the plastic funnel to the metal neck. I usually remove them all and make more room to move it out of the way. Now to pull the bed get 4-6 guys or more if you want, 2 good strong guys or more works, a cherry picker, or some wood and blocks. Now with the wood it only took 2 guys maybe 3, raise the bed, slide the wood between the bed and frame, we used a 2x6 8 ft long or longer or a landscape timber. Once it's in between the two stack blocks, we used 8 inch concrete blocks laid "web" up like when you build a house, in other words holes facing up. Stac them on each side by the tires, not touching the tires though, raise the board stack a block on top, go to the other side and do the same, repeat until the bed is high enough to clear the tires, then you can drive out from under the bed. Just be very careful. if you got the man power or form of lift use it. Now you can finally start on the cab corners.