Here's your first problem:
The mustangs are going to outbeat your car. Problem is you don't have the gears to do any sort of mustang hunting. If your running that low of a gear, numerically mind you, then you are much better of going with the TH350. I will bet you 50$ that if you put that 2004r in your car with that gear selection in the back, you'll never use the 4th gear and barely get any use out of the 3rd gear.
I ran my sbc 350 with a 350 transmission and a 2.40 somethin gear in it and would be doing 70mph @ 3000rpm in 2ND GEAR. That doesn't include the lower rpms when I started with my stock 2.29 gears. If you plan on doing any kind of street competition, you need to address the rear gears in your car. If it's a peg leg, you need posi-trac.
If you do upgrade your rear end to a posi, then run a 3.42 like the grand nationals did. Those cars ran the 2004r as well and were excellent performers. You could better yet run the 3.73 gears and do even better without seeing high rpms on the highway with that 2004r trans.
I learned real quick that building a bada** engine is nice, but if you don't address the overall combination of your drivetrain, your gonna be suckin to the 4 bangers. Now why are you gonna let some stupid mustangs get to you? There are dozens of those cars out there and I've seen every single variation of them. They can wreck their cars and go out the next day and buy one identical to it. YOU CAN'T DO THAT WITH YOUR CUTLASS! I'm 19 years old and trust me, I know what it's like to want to smoke the living hell out of everything in the parking lot and on the street. Soon you learn that you gain a whole new respect for you car once you start building and taking car of it.