the ball joints are probably what's causing the problem or at least the majority of it anyway. i'd go ahead and replace the upper and lower arms while you're at it, the shop will have to pull the UCA's to replace the ball joints anyway and then you'll have labor to change the ball joints and the control arm shafts so you might as well go ahead and save yourself some labor charges and just replace the entire control arm. BTW, the lower ball joints aren't service seperately you have to buy the entire lower control arm anyway. definitely go ahead and do the strut rod bushings if they are original or haven't been replaced in the last ten years or so. you don't have to replace the sway bar but you can if you want a bigger bar a 1 inch sway bar will work just fine.
if you want good quality parts that will last a long time check out
www.opentrackerracingproducts.com he can set you up with a kit to do everything you need and his blueprinted stock control arms will keep you from having problems later on down the road. i should have gotten them for my car but i found a "good deal" on a kit with uppers and lowers on ebay that was cheaper, i ended having to get new lower arms because the kit had 67 control arms and they are different from 69 arms and the upper arms i had to take apart and redo the shafts because they weren't centered and the bushing kept trying to bake out when the arm moved up and down in the car. i will never buy new suspensions parts just because i can get a "good deal" on them ever again.
while you're at it consider getting some of his roller spring perches as they will improve the ride a bunch on your car. i have them on my car and absolutely love them, i'll use them on every car i get with the same suspension, unless i do a coilover kit (no spring perches with them) but i don't have that kind of cash so roller perches it is. you don't have to use the roller perches but if you have the money for them they are probably the best improvement for the money you can do to an early stang's front suspension, hands down and not juct from a performance aspect either, they will make any suspension work better because the free the UCA, spring and shock up to do their job better, the stock rubber bushed perches have way too much bind in them to allow the suspension to move freely.
if you don't plan on doing driving your car really hard through corners you can probably just keep your stock sway bar but if you plan on having some fun in the twisties then i'd upgrade to a 1" bar.
