early 70's Mopar towing questions (MPG, Chrysler, wagon, 2000)

[rlrl]

I was just browsing a cool fuselage Mopar site and on the Chrysler Plymouth towing brochure chart it shows that a Valiant/Scamp/Duster can tow 2000 lbs with the 225 6 but to tow 7000 lbs a 440 V8 4 bbl would be needed in the Fury, Chrysler or wagons

Knowing that a 1973 Plymouth Custom Suburban got 7-16 mpg in normal driving and 13 mpg on a 300 mile trip, how much would mpg drop if the same wagon with a 440 4 bbl was towing 700 lbs?

The brochure said mpg drops a lot but i wonder how much