Highest MPG V8?

[sk6strng]

My commuter car for work is an 86 Honda Civic si hatchback (1.5 w 5-speed manual trans, 200,000 miles on the odometer). I drive this car light and dont wind up the revs, also have plans to swap out my 5th gear to the 85-88 crx hf 5th gear (taller) to drop the overdrive rpms for better fuel economy.

Going for high efficiency in this car is to compensate for my 56 Belair 9 passenger wagon.

The wagon is a brick. It runs a 1970 vintage Corvette 5.7 litre v8 and 700 r4 overdrive trans into a 2.73 rear gear. (Headers and dual exhaust)
I am running Michelin Primacy x 245 series tires meticulously kept at 35 psi.
I guess that this 57 year old car gets quite poor fuel economy...dont know for sure since the speedometer is inoperative. The engine turns just under 2000 at 70 mph.
But check this out...The car is generally used with three or more occupants in it, often upwards of 6 people with my two 9 year olds and their friends.

It does merit mentioning that if this car did not have three rows of seating many of my weekend car trips would require two vehicles and two drivers.

Any tips for saving fuel on the wagon are always welcome (comedy appreciated)..
Thanks and have a great day!