i hear the backspacing is different on a 3rd gen from the front to the rear.

this is important to note if i happen to find a decent set of replica irocs. most that i found online have the same backspacing.

would that bother performance or safety?

 

3rd Gen wheels are either 0mm or 16mm offset. Compare to 55mm offset on 4th Gen wheels. Here's a table of wheel dimensions, including offset and backspace:

http://www.skulte.com/adapterfaq.html

 

thank you very much, that was informative and exactly what i was looking to find out.