We installed a 1995 Dodge truck 5.9 with the A518 overdrive in my wife's 73 limelight cuda. It has 3.55 gears and the cruise control system out of the Dodge truck. It gets 29 mpg with the cruise set at 70 mph with no a/c and the windows down. Stock truck computer. We were surprised...and delighted.
Now I need to put the 5.7/5-speed auto that I bought into one of my other cudas.