I agree with shelbydogg, cut off wheel, welder, and you can fit almost anything you want in there.
I'm working on some Supra seats for mine right now. They have nice side supports, thigh supports, adjustable tilt headrest, fore/aft position, tilt/recline, and three bag lumbar adjustment. For $50 for the set, I'll make them fit.
Almost anything you get will need the inside track spaced from the floor differently than the outside track. My tape put it at 1.5" difference.