1973 Dart Sport Improvements

A 12.0second quarter is a P/W (Power to Weight ratio) of .108 with SuperStock unlimited suspension.
With street suspension you'll need to target about another 1/2 second; so.... .120
If your car weighs 3600 with you in it, then .120x3600=432 hp. That's about what you are gonna need.
And the gears,tires,wheels, stall, etc to optimize it.
Your speed to go with that .108 is about 110, so after your engine comes back from the dyno-shop you can eyeball the power-chart and find the rpm of peak-power, and select the gears you need.
That engine is gonna need a pretty big cam, so the gears are likely gonna come in around 4.10s/4.30s , and a maybe a 3800stall (I'm guessing),so this would not be my idea of a good streeter. Without the big cam, you're gonna have to spend the money on the heads.
Don't forget the support works. At this power level, the cooling system needs to be top-notch. The fuel system and ignition systems will also have to keep up; and the trans has to not blow up, etc.
Every 10 pounds you can lighten your car is worth about 1 hp. So if you can diet 150/180 pounds, that's about 1 cam size.
As to weight;the heater is ~16, fold-down rearseat~64, 73 non-shock-absorbing bumpers and brackets gotta be at least 40/50 apiece, one steel wheel weighs about what two mags weigh. The power-steering system is ridiculously heavy; dual 3" exhaust with a pr of 3-pass long mufflers is about 72; Forget A/C.
the point is this; 200 pounds is doable, even 250, but now yur leaving streetable behind. And driving to the track, then dropping the exhaust, and unbolting the bumpers, is not a lot of fun for me. Not to mention no heat or defrost. And without the fold-down rear seat; I guess you'll be staying in a Campground unless you managed to convince your wife to come... then it's Motel only anyway.
Low12s/hi11s on all motor, ain't cheap with a modest engine.
But just about any old 383 will get there by Nitrous.... even with your 3.55s and 3000Tc.Crank it up!.