Thanks to Dads50 and Brad. I was just out in the garage wracking my brain (again) trying to figure it out. I hadn't realized that the rear most cross member was actually cantalivered over the rear of the frame rails. referring to the pics again, it all starts to make sense.
And Dad, now that I have the dimensions for the "wood" blocks, I can really get moving on that portion of the project. Special thanks!
