If he wants to go all out, then yes, he can get the complete tuning software... He would really have to know what he is doing in order to tune the car correctly as far as tuning software goes... Which most people really don't know how to do things like that and that's why we pay hundreds of dollars for dyno tunes - to leave it to the professionals to do. If he's got that kinda money to throw around, go for it, but a simple handheld tuner should give him what he is looking for.
If he goes SCT or diablosport, he can just upload a canned tune or one of the tunes that the AM guys send him and he will see an increase in power. Also, from what i have read is that SCT and diablo are both pretty much idiot proof and you can adjust some of the tunes yourself to increase spark or advance timing w/o having to worry about detonating or pinging (or if you do, you just keep decreasing the spark/timing until the pinging stops). In my opinion, i would just stick with a canned 93 tune and run super (93 octane)..
Unless you know what you are doing and have an A/F gauge, don't alter the tunes... A canned tune will net you quite a few horsepower, especially with the s197's from what i have heard/seen... Intake/tune on an s197 and you get 10+ rwhp/rwtq am i correct? That's a nice gain. Especially when you have an automatic and you can bump up your shift firmness with the tuner as well. It will feel and probably be much quicker. (although idk what tranny's the auto s197's have... they may already shift hard/quickly)
When i had my automatic v6 mustang (2001), i bought a used diablosport for cheap and i removed the speed limiter (just for sh*ts and giggles), turned off my traction control, and raised up my shift firmness, as well as uploaded the diablosport tune and it was a whole new car... Just raising the shift firmness was awesome. Car was more responsive as well..
If you ask me, i would just stick with getting a USED AND UNLOCKED SCT or diablosport (whichever you can find cheaper) and loading a tune to your car (you can find them used for sale on mustangforums.com all day long).. Do not raise the rev limiter or alter anything like that unless your car has cams or a high reving intake manifold and many other supporting mods that can handle the increased RPM's and you are on a dyno seeing where your car makes power up until... That's when you bump the rev limiter up. Otherwise, you'll only chance doing damage to your car...
And the AM code is 6%, not 5%
EDIT: And a tuner is a great investment. When/if you get gears, 10 minutes of your time and you can upload your changes via the tuner to tune the ECU for any gear selection you have installed..