The factory book says the vacuum advance only does 11 degrees.
With no centrifugal advance I would think anything would be better than the original. And spending money on an electronic unit for a stock distrib is a waste.
My F1 V8 gets me around 10 mpg with a 3.5:1 rear end at 60 mph.
If I had something that would advance the spark more at cruising speed.............