Honestly I would have to see this car to make an honest judgement. Miles really don't mean shit with these cars, the overall maintenance and care means WAY more. I have had around 16 foxbodys and have looked at 100's for myself and friends. I have owned high mile ones, stock ones, low mile ones, modded ones, etc. Most of the cars for $4000-4500 range are POS that have not been taken care of and driven all year round. IF this 93 has been taken care of and not driven in winter ever I'd throw $5000-5500 at it in a heartbeat.
My cousin's 89 GT with 175k miles was cleaner underneath than my 39k mile 88 GT was. The thing with super low mile foxbodys is that they have sat way too much which is worse than being driven.
With a SC'ed car I would be careful because just from the sounds of that ad the guy has no clue what he is talking about. And why was the motor changed???
My 93 GT had 74k miles on it and sitting next to a 9,000 mile 93 Cobra at a show you could not tell they were not closer in mileage. It is all about how the car has been taken care of. I'd take a bone stock 100k mile car over a piss pounded modded to hell 50k mile car any day of the week.