I have had several SVO's, all 4 years (84, 85, 85.5 and 86). The 86's are the fastest.
None of them were really reliable. Seems like it was always something. Kick a rod out. Distributor gear. Aux shaft gear. Timing belt once or twiced. 7.5 rear end had cone-type "posi", which was weaker than the clutch style, and you can't get parts for the style nearly as easily as you can the clutch style. Front ball joints are non replacable on all SVO's, so if they're worn, you're gonna be doing a lot of thinking on how. The transmissions are different. 84-85 had a 4.03 low gear which sucked. The 85.5 and 86 had a much nicer 3.50 low gear which brought the ratio split closer together and made the car faster and more fun. Wiring around the engine tends to crumble particularly with the early units. K member is a little different. Seats are unique. There just is a lot of things with the SVO's that made them "special"; yet hard(er) to find parts for. There weren't that many made to begin with. They are STILL a 4 cylinder Mustang and thus don't carry much value unless VERY low mileage and bone stock, and beautiful showroom new, and then you might expect $10k. A 5.0 in same condition brings more every time. I don't know why; most of the SVO's were neat cars in their day and somewhat rare. I ain't seen one on the road in gosh, 5, 6 years?? Long time.
12 second driver? Possible...HOWEVER, you'll need to go into the engine. Do the bore/hone deal, and put good pistons and rods in it (CP/Carillo). The stock rods are ok but they get weak at 300hp+. Once you get past about 275hp, you're gonna be looking for a different turbo to support more power. Then the ECU and VAM are done by about 300hp. Figure 300hp as the absolute uppermost limit for the stock stuff and it's not likely to put a stock SVO into the 12's with 300hp; and even at 300 you're probably gonna need a mildly ported head and a little more fuel pressure. 2.3's are fun to play with but they are expensive for just having half the cylinders as a normal Mustang. The bad part: set of rods is $500 and set of 4 pistons is also about $500. It's almost cheaper to build a 5.0 and then you have to address the turbo, header, intake manifolds, engine management, etc...it adds up, quick. That's why I left my current 2.3T project a mostly stock engine with bolt-ons (exh, intake, and roller cam to replace the worn out slider cam).
--BUT--
Even with all it's downfalls, the little 2.3T engine in the SVO is still kind of cool, it is absolutely FUN, easy to work on (for the most part), and built properly they are mostly reliable given the fact that the block is so lightweight (the head & manifolds with cam weigh as much as a bare block does!), and they handle pretty good for what they are. I do not currently own an SVO. They are too "special" for me to want another one, but I do have a '93 coupe, with an SVO 2.3L turbo, did the
suspension, dampers, steering rack, then put decent seats in it from a 2009, and made it my own rendition of an SVO, but uglier. Clearcoat gone, centercaps long gone, ain't washed it since I bought it (the rain washes it for me), surprises a LOT of unsuspecting folks with how it hits hard at 2500 rpm, it's honestly like a light switch. Off (about 1800 rpm) is about 80 hp. On (about 2500 rpm) is about double, maybe more.. It will (if I let it) eat tires when it hits in 2nd gear and occasionally third. That's at 18 psi, which is all I need. 30 mpg too. Lots of fun but it's on borrowed time as far as reliability goes, 20,000 miles and the only problem I've had out of it in that time is a leaky valve cover gasket, a leaky water line, and currently has an oil leak up top that I haven't found yet....probably the oil separator on the valve cover. Minor I know. Last SVO I owned ate a distributor gear, then an aux gear, then timing belt. It went from the belt to busted rod and windowed block, took about a year. Built another engine while the TRW pistons were still available (they are no longer) then broke the rear end while negotiating a turn, 5 mph, barely creeping, just bound up and went bang. Fixed it with Ebay parts and sold it. It was fun but too much work to keep running. They all were like that, if something wasn't broken it wasn't being driven, and it was always something.
SN95 stuff is much more comfortable, reliable, faster (though suprisingly not by much if you compare a GT to a SVO), handles almost as well, etc. The newer they are the better they get in a lot of ways, but the more expensive they are too.