Jim,
The only modification I did was to the passenger seat. If you look at the pic above, right where the seat belt is on the passenger/tunnel side, I took a BFH (big fuquing hammer) and gave it a whack or two. I did use a piece of 2x4 between the hammer and seat, maybe with a piece of cloth on the seat side. I only had to whack it in about 1/2" or so. Nobody notices but me. No modification to the drivers side. The seats have a steel tubular frame so they are easy to bend.
Now, moving the seat cushion away from the sides will expose a piece of square tubing on each side of the seat that runs from back to front. This is where the mounting holes will go. I drilled through the tubing and through the floor and mounted the seat right to the floor. I used 4 bolts per seat/two on each side.
The seats give you great support but could use a 'slight' more lumbar support. They are not by any means uncomfortable but for rides over 3-4 hours I'd roll up a small towel. When it comes time to recover I'd have the guy build it up a bit.
The whole seat mounting process went smooth and uneventful.
Roscoe