will have to whip out the rivnut gun and make some new mounts for it
Rear mounting holes are not rivnuts in the orignal setup though... There are steel plates bonded into the rear chassis crossmember which are threaded and where the bolts originally screw into. Rivnuts would likely not be up to the task of sustaining the load from a crash which is transferred from the seat belts to the seat frame/rails and then down to the bolts tha hold the seat in the car. The front crossmember holes have threaded inserts fitted underneath during chassis production to spread the load on the ali rail. In both cases there's a void between the ali floor sheet and the inside of the chassis beams, so if you intend to create new (seat) fixing points you may want to cut small access slots/holes in the ali floor sheet under the (hollow) chassis cross members where the seats bolt onto and then fit bolts and nuts to keep the seat in. Then just use some rubber bungs/plugs to seal the holes again.
No biggie as it's often done for fitting race seats and harness anchor points. I'd just advise not to use rivnuts for seat fixation in this application.
Bye, Arno.