Alright, number one:
You should only have an old Corolla for a project car. They suck for daily drivers. They are all 20+ years old and it shows. You have to do a complete overhaul and recondition to make them be reliable.
Number two:
The SR5 came with a SOHC carburated motor called the 4A-C. Makes three horsepower. Gay. Also came with different rear end and suspension components, tiny discs up front with drums in the rear, lame gearing.
The GT-S came with a DOHC 1.6 liter called the 4A-GE, all wheel disc, and shorter gearing. They also have a different rear end and clutch type LSD was an option.
If you want a performance Corolla, the AE86 GT-S is the best choice. The SR5 to GT-S conversion is a huge pain in the ass and will cost you more than to just buy a GT-S in the first place.
Great project cars, shitty DD's. Oh yeah, check out hachiroku.net. That site rocks.