[bushpilot]

I think you'd have to be pretty short to be able to SIT up in any cab over bed.
Our coach doesn't have the (occasionally) optional 6 inch extension (were already 13' 1" to the top of the air conditioners).

I don't know why you'd raise the height in the front & not do it in the rear or all the way back - certainly aero dynamics won't suffer.

regardless of what you do - you really should keep it under 13'6" (standard height of tractor trailer Trailers) - anything over that height is gonna limit where you can fit. IE the oklahoma turnpikes are height restricted to 13' 6" (anything more and you're gonna be pealing the top off as you go under bridges).

As for the pass thru - anything is possible & they make accordion gaskets to seal the cab to the box (almost all our conversations have 'em)...if the opening were too large after the window removal some light welding and body work could finish it.

I'd remove that center seat for the freedom of passing / walking thru to the "house".