You're not comparing apples to apples, as the two cars had vastly different standard equipment.
70 Mach 1 base is 351W or 351C 2V, FMX iron case auto, 9" rear, fiberglass hood scoop, Deluxe interior with console - for 3351 lbs.
71 Mach base is 302-2V, C4 auto, 8" rear, base interior with no console and a flat hood at 3172 lbs. Add the 163lbs for the 351-2V to a '71 and you're getting not only a heavier engine, but an iron case FMX, bigger radiator, scooped hood and a 9" rear. Now add console (12 lbs) and Decor Group (15 lbs) to even the option load - which puts you at 3362.
That's the point of the entire post is that these cars were not the "porkers" that they were portrayed as.
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