I haven't really been able to find any information on the stated MPG of any vehicle made in 1984 or earlier, as the EPA web site starts their listing with 1985, and I realize that part of this is that they changed how they test vehicles around that point, but it would still be nicet to have numbers to compare one old vehicle to another old vehicle.
Would something like a Buyers Guide have that information?
Probably your best bet is to find old magazine and TV commercials such as this 1984 Ford Tempo. "Tempo has the world's most advanced automotive computer. It contiunally monitors 7 vital engine functions for maximum fuel efficiency!"