In 1997 they made 372 total Saleen Mustangs: 113 Coupe S-281, 13 Coupe S-281 Cobra, 21 Coupe S-351, 196 Convertible S-281 (including 88 Budget Rentals), 5 Convertible S-281 Cobra, 19 Convertible S-351 and 5 SR's
The S-281's recieved high performance spark plugs, high flow air filter and Borla exhaust to the tune of 220hp. The supspension list is lengthy (wheels, racecraft springs, shocks, swaybar, etc....) It used the stock Mustang GT tranny (not sure if that was T45 or what) MSRP $29,500 coupe & $33,900 Vert
The S-281 Cobra's were stock SVT as far as engine & tranny - 310hp. If that is more than a stock SVT I would guess they do the same plugs/filter/exhaust upgrades, but I don't find anything about that specifically in the book. They received the Saleen appearance and suspension treatments. MSRP $36,900 coupe & $39,500 Vert
All of the S-351s were Vortech supercharged to the tune of 510hp. They also got a B/W 6spd tranny, Saleen hi perf pressure plate & clutch, balanced & custom drive shaft, 3 core radiator, 2.5" stainless 4 way cat high flow exhaust, high vol fuel pump and a few more goodies. These cars were truly BEASTS by 1997 standards

MSRP $53,500 coupe & $57,900 vert.
There are subtle ways to tell them all apart. The S281 has the stock GT hood with small oval vents toward the back. The S-351 has a raise composit hood with the same oval vents, plus two larger extractor vents in the middle. The S-351 also has a larger wing that sits up/off the trunk lid, whereas the S281 wing is a tad smaller and looks like an extension of the entire lid. S281's got 150 Saleen Speedos and S351' got 200.
And the Cobra would be recognizeable by the Snake on the side of course