Did a final fit of the 98 Silverado 40/20/40 seats in my 69 K20 yesterday and then that evening I started installing the insulation. I made some re-enforcement brackets/plates for the seats as they have the integrated seatbelts and I have heard the floor needs to be beefed. The mounting holes on these seats to not match the existing holes so what I did was add these plates to the top of the floor and then I have also made three plates that go under the floor. There is a section of C channel welded to the front bracket that the middle seat attaches to. Underneath the truck I have this plate that is in the raised area below the front bracket. Then I have two additional plates that both go perpindicular to this plate. One is about 5" wide and connects the front seat bracket to the rear seat bracket nearest to the transmission. Then I have a plate that is about 1 1/2" wide that connects the front seat bracket to the rear seat bracket nearest to the door. My intent is that with these brackets tied together from the bottom of the floor to the top of the floor, I have reinforced the floor where the seats bolt in. Got some of the insulation installed last night.