Overdrive is the way to go. Not just for gas mileage, but also
1. Higher speed top end (with your truck being a 1971 model, you already have front disc brakes from the factory so stopping won't be an issue).
2. Lower engine RPMs (means less wear and longer engine life).
I have an overdrive behind a mildly built 292 in a 66 short stepside p/u. Gas mileage is still not good at all, even with sensible driving - I'm sure it's the big @ss 4 barrel I have on it!
But I love it. I wouldn't trade being able to cruise 80 mph on the interstate at only 2600 rpms for nothing!
-ftyler
