Basically any time you reduce weight transfer you reduce traction, so to get your car into the 12's with sport suspension would take quite a bit of horsepower (to make up for the spinning you'll do all the way down the track).
Eibach lowering springs (sport model...not the stiffer ones, make sure to get the progressive rate springs if you want it to be drivable everyday) are a good idea and as for adjustable struts and shocks i think you have to take out alot of them to adjust them and some of the ones you adjust on your car can be kind of vague in terms of adjusting (from what i've heard). KYB or any name brand strut or shock should be good, i'd personally just get a sport valved shock and leave it be (how often do you want it to ride like a lincoln?).
Also, make sure to get Caster/Camber adjustment plates and get your car aligned because no matter how well your car is set up, it's all a waste of money if the tires aren't contacting the road all accross the tire and this is a common problem when you lower a vehicle because you get a (positive???) camber change which causes the inside of the tire to wear excessively and causes wandering when cruising down a road.
Subframe connectors from what i've heard are basically the first thing you should do because no matter what there's no reason not to have them. That's the first thing going on my '89 GT (have the subframe connectors ready to go, just need to weld them in). Since your into corner carving a strut tower brace, from what i've heard help alot in keeping the strut towers from moving and causing hopping or change in caster/camber because of flexing.
Good luck and happy mustanging!
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previous name: 84stangLX
'84 Mustang 5.0 LX
my LX
'89 Mustang GT
my GT