SD cars DO make more power than MAF cars; i would by no means say that it would destroy a MAF car, as the difference isn't that big, but the SD is faster. if you were to take two cars, an SD and MAF both in good, stock condition the SD would make more power on the dyno, and run the 1/4 faster, no questions asked.

Personally if i were to buy a car that's basically stock to modify it would be a 5.0L LX notchback 5-speed, unfortunately they're alot harder to find than regular Hatchbacks and GT's. They're lighter, more rigid structure and i personally like the look of a notch especially one with skinnies and fatties on it.
I would personally also recommend an '89+ because of the fact if you get the car fast enough in the future you won't have to buy the mass air conversion kit because you'll already have it.
Here's in order from heaviest to lightest the kind of 5.0L stang you might be interested in:
LX notchback
LX hatchback
GT hatchback
LX convertible
GT convertible
If i were you my first mods would be:
better rear end gears like 3.55 or 3.73:1 gears for a manual or 3.73 or 4.11 for a manual. Manual trans. equipped cars are faster than the automatic ones at the same power level and i've heard that the AOD needs quite a bit of work to shift quickly and when you want it to.
The next modification i would recommend is subframes connectors because even on a stock vehicle i hear it stiffens the car up substancially and makes it rattle less and handle better on extreme cornering and acceleration.
Then i'd recommend some sticky rear tires for the street and after that some engine mods.
So far there's been some really good advise from everyone and you've heard quite a few opinions so only you will know what you will want performance wise from your car. Good luck, i hope you find something you'll like.

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previous name: 84stangLX
'84 Mustang 5.0 LX
my LX
'89 Mustang GT
my GT