Hey Jonatahn. I'm assuming you are correct on the parts needed for the conversion, but I don't know for certain. When I bought my car in 2010 it already had the GXP front clip. Lucky me! If I had the money I would go with the Commodore E3 front clip.
What's up man! Haha glad to hear you are liking your new Solo axle backs! The GXP diffuser will definitely make the rear end look better too. Hey at least the ball is rolling and hasn't frozen up yet like mine will pretty soon due to house purchase and wedding. Oh well the modding will just shift from the car to the house!