I have been trying to make more room behind the steering wheel and also trying to get more leg room. I believe I found a Chevy bench seat that I think will help gain a couple inches. It dawned on me I can gain even more room if I ditch the fuel tank in the cab and mount a 30 - 50 gallon tank to the LH side of the frame under the bed. Any suggestions on what vehicles to look for as a donor and best way to install a side mounted saddle (?) tank are greatly appreciated.

 

I'd be interested in knowing this too

 

If you remove the in-cab fuel tank, you will not gain any legroom, due to the angle of the lazy back.

More than likely, the seat is as far back as it will go.

 

I agree with Bill! I removed my in-cab tank for other reasons but can't say it provided any more leg room. At 6'3" I would like a little more leg room. But like Bill points out the top of the seat back contacts way before the bench would hit the tank. In my gallery there are photos of the fuel door I added when I put my fuel tank between the rails. If you use the cut-out from your bed side you could probably attach it to just about any flip open fuel door. I used an electric one from a Lincoln.
Good luck, show us what you come up with.