It is true that 1993 was the first year for SVT and the Cobra as we know it today, however Ford did offer a Cobra package early in the fox run, though it was mostly a bunch of stickers rather than an up-level performance package. (at least 80-81 Cobras and 82 GT's had the 79 Pace Car nose...one of the best looking fox noses ever)
It would have been cool if you could get any Ford engine in a Mustang, but the only engines available early in the fox run were Fords small mediocre engines...no 351's or 400's here...but remember even the bigger motors of the day were pretty anemic
79 - 2.3 I-4, 2.3 I-4T, 3.3 I-6, 2.8 V6, 5.0 NON-HO V8 (Cobra = 2.3T or 5.0 V8)
80 - 2.3 I-4, 2.3 I-4T, 3.3 I-6, 4.2 V8 (Cobra = 2.3T or 4.2 V8)
81 - 2.3 I-4, 3.3 I-6, 4.2 V8 (Cobra = 4.2 only)
82 - 2.3 I-4, 3.3 I-6, 4.2 V8, 5.0 HO V8 (No more Cobra, most GT's got the 5.0, a few came through with the 4.2)
Mind you that the most powerful engine here was the 5.0 HO of 1982 and it put out a whopping 157HP. This, however, is the car that brough performance back to the automotive world...and the rest they say, is history.
On topic to the thread though, the best advice to achieve you the most fun and ease of modification is find the cleanest 87-93 ORIGINAL 5.0 car you can find, and then go crazy. 79-85 can be made great but in many cases you have to modify the car in order to modify it (IE: change trans crossmember to clear dual exhaust) Like i said, this board will give you all the info you need. Now get out there and find a stang...then make it the car of your dreams!!!