i wouldnt be putting so much of a system into a chevelle. with a pair of L7s the car is going to sound like its going to want to fall apart, they didnt insulate cars very good back then. get a nice deck, for it(mounted under the dash so you dont cut up the original dash) make some kick panels to hold a nice set of 6.5 components. (i have boston pro 6.5s are nice btw, verry loud) get a good amp to push these(at least 150 rms per side, preferablly about 200)
see how you like that, bostons put out pretty good midbass. after that i would suggest a pair of 10s for sound quality. JLaudio W3s are pretty nice, also adire shivas seem to have a hell of a rep on them.
the reason im suggesting all this is i was in the same situation as you a few years ago. 17 years old in my 72 duster, i had 2 L5s with a PG Tantrum 1200.1, 2 sets of infinity components off a pioneer GMX-924. it was loud, sounded great to me and everybody else around me. but it rattled the shit outta the car and made it sound pretty horrible outside unless you were a block away. most of the time i didnt even use it, just low volumes and enjoying the sound of the 360.