Gene, as to getting the seat back a couple of inches.
since you have the gas tank in the dakota location, and out of the cab, is there a couple of stiffening ribs on the back of the cab wall you could remove, allowing the seat to touch the back of the cab ?
just thinking out loud here, as i am not familiar with those year trucks.
or maybe you have already done that, and i either forgot about it, or missed it when you said you did that.
beer