My truck has a 3.08 gear. I can drive it to work and not go over 2000 rpms. Yet it still gets 8 mpg. The sbc in the same situation gets around 11 or 12. Seems like enough gearing to me.
It's no mystery that a BBC is not an efficient engine. I'm just letting the original poster know that BBCs are thirsty. However, since it is not a daily driver it will not matter that much.