I use a set of Kyouu Seat subaframes. These mount directly to the floor pan using the original seat mount points. There was a guy selling them in Canning Vale on Ebay.

Then bolted to them are some seat side mounts (forget brand, but these are all more or less the same thing). They connect dir3ctly to my OMP seats. I could have opted to also fit sliders between the subframes and the side mounts. But opted not to because race car with fixed backs.

You could also go for a weld in seat base aswell.

__________________
Doing it for all the wagons out there