Going back over this I used a 10x3 for the frame plate. Next time I would use around 12" or more. The front bolt location is fine and nothing interferes. It could move forward as far as you really want to go.. The aft bolt was a pain as their where multi layers of sheet while only cutting through half of one. Once inside the rail there was this plastic stuff filling the cavity. Easy to cut with hole saw.. (That didn't help me till the 3rd hole.) Routed around with a rotary file took care of it. There was also a 'hump' of sheet metal inside even the hole saw did not like. Might have been the end of the nutsert strip for the trans mount. Whatever it was a F'n PITA to cut.. Move down about two inches no problems..