Right, the base I have here is for an Astra, unfortunately the Nav GPS connector is different and the angle of the Dipole is going to be wrong for an Omega estate (although the Prodrive adaptor would correct it).
You could concievably cut the connector off this one and crimp the correct one on but that will be a bit of a trial to obtain the correct plug (been there got the T-Shirt).
The amplified section of your base appears to have had the +12v feed wire cut off in your picture. If the radio reception is OK I think i'd just leave what you have there and add a seperate GPS mouse directly into the unit. This is one has the correct connector on it for direct connection:-
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=230526593445&ssPageName=STRK:MEWNX:ITYou could then just tuck the mouse up under the dash as long as you don't have a heat reflective windscreen.
Hope that helps
PS. H21 I might be able to make use of that antenna and base if you still wish to sell it?