53chev: Sometimes the frame is tweaked a bit and the block height needs to be adjusted. The rear sill bracket is 4 inches tall. Each of the other mounting points needs to be just high enough to make the tops of all the cross sills level with each other and the top of the rear sill wood mounting surface. Shave your blocks if necessary to get everything level. Also, check the splash apron clearance to the bed side as that is controlled by the mounting block height.

Mar-Ktech