Here's Hanks description, and a photo from Whit....

Basically,
the plates were made from 1/8". The rear seat mounts were tied into the roll
cage mounting plates, and still complied with the CCR as regards the max
allowable size for cage mounts. The factory front seat mount pedestal was
removed to enable the seat to sit lower, and 1/8" plate was welded from the
rocker to the tunnel, shaped to to match the floor contours, to provide
reinforcement for the new front seat mounts.

Remember that the stock floors are pretty thin to begin with, and because of
the cars' age, the floors are pretty weak IMO. So, reinforcing the floors
(for the sole purpose of securing the seat, NOT for the purpose of
stiffening the chassis to gain an advantage) is a good idea. I think Whit's
approach was great, since it more widely distributes the load, but it is
time-consuming and costly if you are paying to have it done. So, in the case
of stripped holes, rather than trying to helicoil and reinstall dinky little
stock-sized bolts, if a customer does not want to cost of larger
reinforcements like on Whit's car, I like to drill all the way through the
floor and then use 1/8" flat plates, approx. 2"x2" square, to sandwich the
floor and create a reinforced seat mount. I don't like fender washers
because they are usually too thin and to small in diameter.

sorry.... I'm blowing it on getting the file to show up at a good size. I'll try again later

Thanks Cullen, Hank;

For the picture and description.