I have a 38 Chevy 2dr sedan.
THE FRONT SEAT FRAME, I made a rectangle of square steel, used 3/4'', shoulda used 1'', the width is what was needed to bolt bucket seats to, the length was long enough to bolt the seats to and have thm wide enough,, HINT ,, I had to make 2 frames, because when i put the doors back on, I found i had lots more room to have the seats wider apart.
From the bottom on this rectangle I made angle Iron bracket (maybe an
1.5'' wide) to bolt to stock seat mount holes in the floor on each side of the the car,, (just inside the door).I just remembered I made the frame lng enouggh so these brackets welded to the length. That was how long the rectangle was,, to the seat mount holes.This way the seats had a level platform to bolt to and were higher than the center hump in the floor. I found the seats felt best quiet high up. I think mine are 13'' off the floor. I used 84 Monte carlo leather seats, the car had 4 bucket seats, So no trouble fitting the rears in.