I have dismantled both 29 and 30 tudors. My best recollection is that the seat riser is buck riveted to the subrails and cross rails around the front and sides and through 3 reinforcing brackets all the way in the rear of the floor. Depending on how many times your car has been “restored” or how much rust is in these areas, you might need to search hard for the rivet heads under paint or rust buildup. Once you find them, drill them out carefully. Some are 3/16” while others might be 1/4”. Once the seat riser is removed, the floor pan underneath may be held in with more rivets or, more likely, pan head sheet metal or machine screws. Again, the heads of these screws might be covered with 90 years of debris or rust. Be patient, there are lots of these screws. Once again, probably easiest to drill them out than to try to unscrew them. Once these pieces are removed, you’ll have a good view of whatever repair work you need to do to the subrails. Good luck.
