If you want my opinion of boxing back to the end of the cab, I would not do it, unless you box the whole frame... as it will break a lot quicker with the frame twisting from there back, the frame will crack at the end of the box... I would do an engine mount that fits under the pan from one side to the other, bolted in, this will take that front twist out of the frame, that usually happens when outside engine mounts are used, on just the frame itself, one on each side is too much for a channel frame... With the wide (both sides) type of mount, there is only downward force... same as the stock factory engine mounts were that were in that truck stock... JMHO BTDT
