Thanks John,

I believe we went down this path awhile back but just needed to check. Three inches works for me and if you add the height of the metal you get a little more than 3". It appears that we have a 9 degree cut on the top of the front pan wood support to facilitate the slope of the rear seat pan to the rear frame. It all logically comes together. The sides are a right triangle with a base of 17" and height of 3" using math the calculated angle = 9.8 degrees. I measured approximately 9 degrees. So I am in the ballpark.

Thanks for the quick response, Chet...