ok, I think what I'll do is this....
The seat tracks on the seat frame are 3/4" wide.
I'll buy either 1" or 1-1/4" square bar as a vertical spacer. On both ends of the spacer, I'll cap it with some 18 ga. sheet that I have and maybe reinforce it in the corners.
Thanks for the tip. I'll also be sure to weld another piece of plate on the underside of the floor and maybe weld a nut to the underside plate so that I can take the seats out from the top.