WR Sport back box to standard exhaust
 

Hi I've been looking at getting a used WR Sport back box to fit to a MY1999 Turbo with standard exhaust.

From what I can find
a> The WR Sport back box is "2.5 and, b> The standard exhaust is "2.25 is this correct?

Also read the WR Sport box should bolt straight on to the standard exhaust. Is this true? Or a case of filing the flange bolt holes slighty to bolt them together