Well the answers were kind of varied so I decided to just dive off into the project.
This is an 85 model cab and a 78 model high hump. Both trucks were 2wd. Best I can tell by looking at the junkyards, most newer model cabs like mine (85 model) had a built in high hump or a built in low hump. I could not find a later model cab with a bolt in hump around here. So, I had to use the 78 model bolt in hump. The two floor pans are quite different.
I had to reshape the edges with a hammer against a straight edge to get the contour proper to fit the floor. Figure about 10 minutes of bumping the metal, test fit, and repeat. The floors are similar but definitely not the same. The edges on the sides of the hump had to be dressed downward to make it hug the floor properly.
Lay the tunnel into place and mark the perimeter, then remove and mark a second line about an inch inside of the perimeter mark. That's your cut line.
Hillbilly Plasma Cutter...
Resulting hole...
Now bolt the tunnel in place with 5/16 bolts and nuts with washers on the underside...
Roll underneath and weld the nuts and washer combos to the cab floor.
All in all, pretty easy. Figure an hour and a half to do the work.