These guys have given you good advice. If you are seriously trying to decide 2.3 modded or brand new 05; basically if you can get any other stang before you mod, do it because the 2.3 na is like the slowest and weakest motor ever built by ford I think. So to start with another car would be the best route, trust me, first 2 cars I bought were two 4 cyls, now I own 2 v-8s. Even putting a turbo motor is a lot of work for not much power (been there done that, my turbo motor got swapped for a 302) It would be better to drop a 302 instead of a 2.3 turbo out of a thunderbird. A 302 bolts right in with access to a donor car for wiring harness and lots of small things. One of the first things you need to do is decide how fast you want to go, and if you want to easily get to 15, 14 or 13 second quarter mile times, v-8 is the best most cost effective ruote, it takes lots more time, work and money to get a 2.3 motor there. Also some more advice would be to not dissassemble anything unneccessarily, wait till it breaks, it seemed to me that once I started digging into my 2.3 it just started running crappier, it is a waste of time to try to mod the car to be fast, but it can be made a little peppier. The cars have other good features, being that they look just like a 5 liter you could get things for the car that will easily transfer over to a new car if you buy one (if you buy a fox-body) things like rims, a hood, headlights, tailights, a big car stereo (hatchbacks are good for this they POUND) and other appearance items, then you can build on what you have for a longer timeperiod. OR, if you really really want to make the car quicker: get a 5 speed in the car no matter what, also get some gear in the car (more than what you have , like maybe a 4.10 or 4.30 gear (this will hurt highway gas mileage some, not much you should already have a 3.73, but a 5 peed will help bring mpg back up. Get a cold air intake (dudes idea for a stock 5.0 unit is a good idea) and make tha car get as much cold air rammed into the box as possible, least amount of restriction in the intake as possible is the goal. Is your car carbed? I can't remember if the 89's are or not but if it is, I've been told all you need is a big carbuerator, big cam (ranger cam is good I think) and a big exhaust and supposedly you can reach 200 hp NA, but I have not tried that one. Cam will definately help, bigger exhaust but not too big, the ranger header works too, remove the front swaybar for good straight line performance and front end weight loss (always good to get front end weight into the rear or off the car), battery to the trunk, take out any crap you have in the trunk: spare tire (who needs that anyway?) jack, junk, any weight you can remove from the car will help immensely. Lightweight wheels, low pro tire reduce frictional losses, lower the car for areodynamic benefit (just chop the springs for cheap, no more than two coils max, more will make clearance issues and will negatively affect your
suspension geometry) these are just some ideas that I thought I would throw out to you, some better than others, my advice is to keep reading and learn as much as you can and ask questions, and just do it. Or if you are going to school and plan on one day getting good cashflow, wait till you are out of school and go buy a stang already fast, and THEN modify. Oh yeah, dude who said the 03 cobra bottom end will handle 500 hp is wrong, it will handle over 1000 hp completly stock, take a look at the 2 fastest ones out there (nitous pete and stricly performance), both are approaching 1000 hp and are untouched shortblocks. The 03 and 04 cobras will be one of the best performance buys availible for many years to come.
Hope this helps someone. Peace
Heck it was my wife that told me to start working on the SVO since I have a ton of crap stack up for my cars in the garage. The stuff for the LX with proubly set there until next year since the SVO probly want get done until school starts. Then to top all of that off me and a friend is starting a business that I hope to have running by the end of the year 
These cars will be killing 05' GT for a long time to come and with no Cobra until like 06' the 05'GTs has no one to take up for them 
have fun, you'll be learning and not even know it, and before long you'll be a pro
