Making a Slant 6 look, and sound cool

Just my personal opinion (your opinion is just as valid), it's a 6 banger. It's never going to sound really mean without spending a lot of money, and then it'll be false advertising :)

Also I'd say that a 70 Dart isn't a muscle car.

A car of that vintage is so old, that if you want to get girls to dig it all you have to do is make the car back into what it originally was... just make it a nice, clean 1970 Dart and it'll be the coolest car in your school. Detail the engine bay and the Slant Six will look better than any modern engine.

So I'm just saying, instead of trying to make it like what everybody identifies as cool (big mean fast strong loud 8 cylinder), realize that what makes the car so cool is that it's still around 45 years after it was built. Make it as much like it was in 1970 and it'll get more and more cool the older it gets. You can always do little customizations too like small decals, or tint if you keep it respectable, or a nice set of rims (the right size for the car!)... or dual exhaust, or whatever but keep it clean and simple.

Just my .02!