i just got a ba fairmont and wont 2 know if i can put the xr6 front on and keep the grill as its chrome

G'day, unfortunately it's not possible. To change to the XR front you need the following, XR head lights, XR Bumper, XR Lower Grill, XR Driving Lights (optional) and an XR Upper Grill. You can get the full CHROME Upper Grill on Ebay pretty easily though.
I'm not sure if you go the XR or GT front for the standard headlights (I assume you have the Chrome headlights as well?) whether the standard grill is still used or if you still need an XR Grill. If you want to hang on to you Chrome Lights and Grill I would phone around some of the shops that advertise the XR and Gt fronts for the Standard lights and check up on the grill.