unless you are going all out racing, and then you have to work with in the class rules, factory replacement parts work just fine. check out
www.p-s-t.com for suspension parts for your stang. as for the steering problem, two things;
1: the steering box was likely not centered properly when the linkage was last rebuilt,
2: the last alignment shop do the toe in adjustment all on one side of the steering linkage.
both can easily be redone when you rebuld the suspension.