Too bad you jetisoned the TBI. My TBI '91 4x4 2500 sub 350 gets better mpg (17 hwy, 13 street) than my '79 big 10 qjet 383 stroker. Well, the sub does have a 4l80e overdrive, but weighs much more.
anyway, tbi gets better mpg in general than carbs. What rear ratio? since you don't drive long journeys often, as mentioned in your thread, you may benefit from a low rear ratio, versus a higher one if you do mostly city driving.
That's another thing about my trucks, the pickup has a 3.07 and it mainly does street driving. Wish it was a 3.73 or so, but she will fly on the interstate and get good mpg there, but, street driving = 10mpg.
Now for your one long journey, I'd personally block off some of the radiator if you're not pulling anything (warm engine uses less gas than cold one) and perhaps turn the air mix screw 1/2 turn out if you don't need the extra power. That ensures you don't run rich (but check it first on a small run to see if it will be ok). Check for vacuum leak prior to the trip by spraying a little wd40 around the engine vacuum lines while idling and see if the rpms shoot up. locating a leak around a line or gasket. Let the carb breathe, invert your air cleaner upside down, as I do in my trucks. Gradually build up speed and dont accelerate up hills, just hold steady. Who cares if you lose a little speed from take offs and hills, your mpg will increase by doing so. Check timing before the trip too. I usually advance mine just a tad going against recommendations.
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