We make seat brackets all the time from 2 pieces of angle iron at each floor contact point. One angle bolts on the floor pan with the flange pointing up, the 2nd angle bolts to the seat bottom with the flange pointing down. The you drill holes at each end of both angles and bolt the 2 flanges together so that your seat sits the way you want it to. If there is a radical difference between the front and rear or between the 2 brackets per seat, we use a filler piece of flatstock between the angle flanges.

Hope that all makes sence, it really is pretty simple. Usually 1/8" thick 2" x 2" works well, but if your concerned, you can use 3/16" thick. Keep in mind, most factory seat brackets are only made from 14G sheet metal, and 1/8" is almost 2x as thick. Gene