extended cab m715 ???

Has anyone ever extended the cab just behind the drivers door ??? has anyone ever thought about doing this ?? im 6-2 and 300 lbs and I need some leg room . I have thought about doing this but not sure if it would work . i would like to add about 12 inches . I don't think using a cab from a other truck would work because the turn is so short at that point . I know I would have to build a custom top and have a custom canvas top made . but as for the metal work I have never did anything like this but I think I could do it if I went ahead and tried it . but wanted to know if anyone has tried this and if anyone could give me some info on this ideal ????

Move the seat down and back maybe? I'm 6'7" and 240 and find it ok.

^ ditto that.

I had a bench seat from a old Ford pickup in mine for a little while. Seating position was lower and further back. Probably lower than a stock FSJ bench would be. I was practically rolling around in the thing in turns and my leg was extended straight pushing the clutch in. Arms were straight out when gripping the top of the steering wheel. But I'm a tiny "light weight" at 6' and 230 lbs...
I would have kept the bench but the springs were pretty wore out... Have Lincoln LS buckets in now. Less room now, probably same or a little less than stock seats. But I'm digging the power lumbar supports, very comfy.

An extended cab would be cool... if you just need an excuse to try it, go for it.

I looked into trying this and here was going to be my plan. Still needed to verify a lot but it would have been legit!

1. Dodge 2500 Mega Cab frame with diesel drivetrain
2. 1963-64 Jeep Wagonneer cab
3. M715 front clip and bed

other options:
Move seat mount back. You can go back about 1 to 2". You can also cut the feet of the mount and rearrange them to use existing holes.

Tilt-steering column and smaller diameter steering wheel give much more room for us who have more girth than the average 19 yr old private.

you can also lower the seat base by cutting and rewelding the feet.

I have hummer seat bases and sliders in my truck with mastercraft seats with tilt wheel and 13" steering wheel. It sits about 1" lower than stock. I have plenty of room and a bonus is that I can see out the side window without hunching over.