My '72 Challenger is smaller than a modern Challenger, so, I don't know about the size thing.
When I was looking at building my garage I wanted to layout how my cars would fit in it depending on the size I built. So I looked up the published specs for my Duster and my 2015 Challenger. They were much closer in size than I expected.
1974 Duster 71.9" wide x 194.1" long (without bumper guards) or 196.9" (with them)
2015 Challenger 75.7" wide x 197.9" long
Note that the Challenger width is without mirrors, those add another 10.1". But the mirrors (in my mind) aren't the issue and the Duster width doesn't include them either, so more of an apples to apples.
Yes, almost 4" wider and over 3" longer, unless the Duster has bumper guards (mine doesn't) and then it is only an inch. But not a foot longer like I expected.
A quick google search shows a 1972 Challenger being 76.3" wide x 191.3" long. So a Challenger is actually shorter than a Duster? Ah, I bet the 5 mph bumpers on a 1974 Duster add to the length.
So, looks like an E-Body is about the same length as a '73 or earlier Duster, but 5" wider, and a current generation Challenger is only an inch wider than an E-Body and 6.6" longer.
For reference, looks like a '72 Roadrunner is 79.1" wide x 212.4" long. Definitely much bigger than an A-Body and even significantly bigger than a new Challenger. Not even going to look up a '72 Charger.