I have a 261 bored out .030 in my 51 half ton. I am running a gm MY-A6 transmission (4th gear .73 OD) and a Lincoln 9" rear with 3.50 gears. With P235/75R15 tires, 65 mph is 2000 rpm in OD. I have no problems with hills in OD. The hardest I have ever worked this combo was bucking a 50 mph steady headwind when I was in a hurry. I just left the gas pedal floored and would slow to 60 mph going up BIG hills.
I am running a Carter YF carb from a 235, so I know I am 'undercarbureted'. I have split the exhuast and am running glasspacks and 2" pipes, so there is NO exhaust restriction holding be back. I hope to install a Megasquirt FI system someday, in quest of better breathing. If I drive the speed limit and don't have to fight a lot of wind, I get 20-22 mpg on the highway.
I am running the six mainly just to be different and because it was the easiest, quickest way to keep my pickup running. This is my daily ride for the forseeable future, so I am really into quick, easy, and dependable.
