Started on my rear seat conversion. Kept my original XS front seats for this very reason, just took a year to find a pair of runners for decent money - £30 for a pair
Using the original seat mounting points.
They fit. They are MUCH more comfortable and actually have some support. Also retained the original "seating height"
Secured down to the floor using LR front seat rivnuts across the bottom + two on the aches with some spreader plates. Plenty strong enough
Got to laser cut and bend some panels to finish it off. Fit the door so I can use the underside for storage. Left space for the derv heater as well.
Then paint
Also got a front middle seat which I'm going to try and fit but it's very tight so needs some more thought, if not it'll have to be a cubby box.