All in all it doesnt sound bad but just know that you will be in for some work on any 1600 mustang let alone a 25 year old one. rust is your main enemy, along with other water damage because the t-tops almost definitely leak.
check the front subframes/shock towers, floor pans, torque boxes and in and around the door hinges for rust. check under the dash and in the engine bay for hacked up wiring. is it a 4 or 5 speed? they started putting 5 speeds in a few months into the model year.
The 83 has a holly 4 barrel carbureted solid lifter 5.0 rated at 175hp 245tq from the factory. the 4-speed would be an SROD not known for its stregnth, and if its a T-5, its a weaker version than the ones used later in the fox run, which arent even that strong themselves. stock exhaust was iron manifolds (not tubular header style), a y pipe with a single cat, single muffler and dual tips exiting on the drivers side, and the rear is a 7.5" t-lock with either 2.73's 3.08's or 3.27's and the brakes were a mere 10.06 inches up front. 83 was the only year that the mustang GT did not come standard with fog lights. my first cosmetic mod would be to update it to 84 cosmetics, with the fog light bumper cover and cleaner rear spoiler.
stock its really not much of a performer but it was for its day, and of course just about anything you can do to a later fox can be done to this car as well.
go look at it and if its clean and solid overall, pick her up and get to work!
Well for one thing, the pictures of it are not great. No engine shot, no interior shot, so no real idea what the overall condition of the car is.
Secondly, it's an 1983. Not exactly the best performance around. Small brakes, weak non world class t-5, solid lifter 5.0. Single exhaust, 7.5" rear end. Just not an overall collection of good parts. You are going to be restricted when buying aftermarket parts and will prob want to install later model components in anyway.
If he wants an 1983, by all means buy it. But for a fox newbie, i can't quite say a 1983 GT is a great performance platform for which to start on.