13's is easily achievable with what you listed. I don't think the 70mm throttle body will hurt you that bad at this point. The underdrives, can be costly if you're not careful. Especially since you have a stereo. I went through two alternators with the mac underdrive pullies. I am not knocking the underdrive pullies, cause I know a lot of people who have them with no problems. You would be alright without the stereo if you left the stock alternator pulley on there and don't let the car sit at idle for long periods of time. I take it you have an amp and subwoofers in your car. If this is the case, I'd switch to the 130 amp alternator from a 94-95 GT. The stock alternator is 75 amps and with a stock stereo and no underdrives, it just barely charges at idle. Take that for what it's worth. If you are going to port the heads yourself, I say go for it. If you are going to spend the money to pay someone else to do it, it is not worth it.
130 amp alternator upgrade