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Many trucks did have 4.11, but don't forget about 4.56's; that was the only factory gearing available in many early 4wd's and it is common in the I-6 trucks too. My 66 has 4.56 gearing in it. I have had no problem hitting 75 with my recent rebuild in that truck. I haven't put a tach on it, but I don't feel the motor is "screaming" either. There is definately room on the pedal too.
Well one won't go at all with no engine. When it had the 302, it went over 80 but I was pushing the motor and although I had an Edelbrock Carb/manifold, there wasn't anything special about the rest of the motor. The 69 I'm not sure I'd want over 80 because of vibration. It is kinda nerve racking at that speed. I think I may have an ignition problem related to bad wiring and perhaps crossfireing, I got a little freaked the other night when it missed a 3000 Rpm. Either that or I heard a valve collide with a piston, I'm not sure. That motor needs a shortblock rebuild so it's biding it's time until I get the Brown Truck running. I'd like to try a higher ratio with the 390 when it is healthy.
Anyway I've feel that ignition/advance/small engine has held one truck back, and ignition/wore out running gear/tired engine have held the other one back.