Interesting figures in a car mag I bought the other day.
Had the results of the late 60's early 70s economy runs in "average" family sedans for the era. They were allowed to drive for economy, but had observers in the car to ensure no coating, and reasonable road speeds, driving over 5 days in the Snowy Mountains (lots of big grades)
Ford Falcon GT (351c.i. manual) 24.4MPG (imperial)
Monaro GTS (308c.i. manual) 29.19MPG
Kingswood (253c.i. manual) 28.62MPG
Premier (253c.i. auto - trimatic, horrible box) 27.17 MPG
Monaro GTS (186c.i. - trimatic) 29.31 MPG
All carbed, OHV pushrod, points ignition (pre-emissions controls)
Their modern counterparts are immensely more powerful, but no better in economy.