Your truck and mine are eerily similar. I too am using late model Chevy truck seats with the seat belts built in. I test fitted it yesterday after cutting away the front section of the original seat riser. I left the back section in place. I liked the low position. It made it easier to get in and out. I will probably fab some mounts out of 1/4" plate. Once I adjusted the seat back to the angle I liked, there was no need to cut sections out of the back cross piece. The headrest was already almost touching the rear of the cab. So I will just leave it in place.
I like you creativity on the interior stuff.
