I liked the Monza also! Loved the Mirage version and the Spyder. I actually have several Monza models from when I was a kid.
Ok, so they weren't really "Muscle cars" but with the exception of the Citation, Delorean and the Magnum, those were semi light cars that came from the factory with little smogger V8s in them. Add a little bit of cubic inches and up the compression and those cars can be kinda quick. Pop a 400hp 340 or 350 in one of those cars and it'll be quick. Actually, their size vs weight can be a little deceptive...
I don't know the numbers but that little Mustang II series actually sold really well. But then again, there weren't many choices. A friend had a done up Cobra II, quick little car.
The '74 GTO was cool, a step up from it's Nova cousin IMO, because it came with a shaker hood scoop borrowed from a Trans Am. It could also be had as a hatchback that year.