Today I tackled the high hump transmission cover, it was very straightforward.
I found a lot of different ways that others have installed their cover, but I figured I would share mine as I think it incorporates a lot of the positives I learned from others.
I wanted it to be removable, and used rivet nuts (rivnuts, nut-serts, whatever trade name you prefer). I matched the size to the OEM size, which is 5/16 - 18 washer head bolts. I got the tool from
Amazon, and bought quality rivet nuts and bolts from the local bolt supply place. I didn't use self tapping or sheet metal screws because I don't like when you have sharp fasteners poking through the body. I also did a practice rivet to set the compression distance for the sheet metal, this is important because you can snap the mandrel.
I installed the rivnut first (less risk of deforming the sheetmetal), using a transfer punch to mark the center of the holes in the tunnel, and a step drill bit to drill the correct size hole.
Once all of the rivnuts were installed, I then marked out the edge of the cover and found that I could cut along the existing dimple around the edge. I then setup my plasma cutter and did a drag cut through the trough. There were a lot of warning threads about making sure that you weren't cutting anything on the transmission. This did not prove to be a concern, there is nothing within a few inches on the bottom. I then used a sawzall to cut the pinch weld areas.
I cleaned up the edge with some 40 grit and a file, and primed. I will use 3M Strip Caulk (08578) for the final installation. I will then prime over the entire floor, put down some sound deadener, and then cover with carpet.
I also took the opportunity to clean the transmission and cross member. I found that it was pretty clean on top. I think the major leaks are the input and output seal, and the drain pan. However, I think that most of the caked on oil is from the engine. I think that the truck has been driven without proper crankcase/valvetrain ventilation. I think it has been about 15k miles since someone put on the period correct "275hp" valve covers, but I think they got 2 of the same without vent holes.