47-55.1 Stretching the cab

[8man]

I've seen instructions on chopping the top, and Jim did an excellent write up on making a convertible, but I'm looking to add about 6" to the 54 cab so I can move the seat back a little for some more foot/leg room. I was thinking behind the doors, but don't know where to stop the cut, add to the roof, etc.

Does anyone know of someone who has done this? I'd like to get an idea of what I'm in for before I get too far down that rabbit hole.

I know I'm supposed to finish the 48, but I'm stuck inside for a couple of days and need something to occupy my mind.

Thanks.