Ive heard people say Return to center can be effected by camber, tire pressure, shocks and all sorts of stuff. But the only things that I have ever experienced do it are caster and too tight steering components. (Usually the sector shaft adjustment) Of course a rack and pinion doesnt have the sector adjustment. Not sure if the Delorean rack has some kind in that regards, but most likely its caster. I read where Dave said there is no caster adjustment, but something could be bent. I dont recall if you build is mostly stock, but I think you could effect caster with the sway bar. If you have the Delorean industry lower control arm braces, you could definitely effect it. Some other brands may also do this. I hate to sound like a commercial, but that is one upgrade I really believe in.
If you want to do some caster adjustment, remember the bottom of the wheel should go forward or the top back to give more caster. (And return to center) You dont want to get that backwards.