The issue with trying to keep older parts is that bolts and nuts rust and can be a pain in the butt. It depends what you want to do with the car. Do you want more power later or is it just to make a little noise?
If you want power, you'll need to decat the system or invest in a sports cat... personally I've never seen the point in the expense of one.
If you just want some noise, I'd just get a cat back exhaust, decent air filter and leave it at that.