Well, I lower my expectations (hahaha), mostly from reading about how expecting 400+hp from these 2v 4.6s is a pipe dream. I go with what is listed as smog-legal here. So the JBA shorty headers were the only option, as was the Magnaflow cat pipe replacement, though that thing flows better than the stock set-up for sure (90 degree bends at the cats stock). Same with the headers, and they sound waaay better. Add the dual exhausts (after the 3rd cat) with Flowmaster mufflers and it's the best that stock-approved is going to get. I could go with 3" pipes after the cats but what for, I'm not racing this thing. I'm only trying to get it to where Ford should have had it new (larger Mustang). To that end I also got the transmission J-modded, I have a Truetrac rear, bigger radiator, urethane bushings almost everywhere. Up next is the Mustang hubs and rims and a 1-piece driveshaft.I forget you're here in SoCal as well. You're in the Burbank area if memory serves correct? You're about 1-1/2hrs (west) from me. Perhaps you can provide some insight as to what to do / have done to keep your mods CA legal.
My biggest move will be getting '97 NPI heads and getting them ported with new cams. From what I've read PI heads are much better than NPI heads stock but ported NPI heads are better than PI heads, and as good or better than ported PI heads. So I will go that route. Around 300hp at the end? That better be enough for me because to try for more requires loads of money for something that I will, again, not race. I assume I will have to reprogram the computer at that point. Eventually I will get a new block/forged crank/rods when I'm in the mood to have everything torn out and put back in. Not ready for that nightmare yet. Maybe new pistons especially if compression is an issue.
I want a cool driveable car. That means it's comfortable and sane driving to and from work or on the road for 2 hours. I can't live with a shaking overheating beast that's too loud for my music. A car that my mom or uncle can ride in if we go visit friends somewhere but doesn't bore the **** out of me. Not an embarrassing "What?!" conversation because my passengers can't talk over the roar of the car and the road bumps keep shaking **** loose from their hands because my suspension is set for a racetrack. No thanks.
For the oh **** this thing is scary car I still hold out hope of building up a modernized '71 Dodge Challenger, though if I stuck with Ford I'd get a '70 Torino (Cobra), the car that our Thunderbirds are actually descended from (these MN12s don't say "Thunderbird" at all to me, not like the 2002 reboot). If you look at a '95 Thunderbird and squint you can almost see a modern Torino. I'm even thinking of getting rear window louvers because of the similarity.
One slight change to the passenger side windows shape, a different front bumper/grille/headlights style, it would totally be a modern Torino.