I did this shortly after I got the car. I removed the foil "Bonneville and V8 " from the back and placed a GXP on the left and a Cadillac Northstar emblem on the right. I've had a ton of great compliments on this change as those foil letter looked cheap. Wish I had a picture to share, but I don't yet. Will post one once I finally get around to snapping a shot!

I do not see anything wrong with the badging on the red G8 Pontiac GT
For the record I own a SSEi and wished Pontiac would have used the 5.3 ltr. V8 in the Bonneville
wich would be a better engine than the Northstar.
My reason for this is that the Northstar engines are an alloy engine and for most repairs one has to
install inserts in the alloy block so as not to strip the threads.
I am sure I will get some responses but I do have the repair manual for the Northstar engines so I do know what I am talking about.
I am sure my next car will be a Pontiac Grand Prix with the V8 engine if I can find the right one.

You do know that the 5.3L V8 LS4 engine has an all aluminum block and heads, right?

Yes but IMHO it is a better designed engine and also a newer engine.
Keep in mind the Northstar engines date years back.

I know the 2006 and up Impala SS has the 5.3L V8!!!! I was going to get a 2008 SS till i found my Bonneville GXP 05!!

Yes and I had a look at an Impala SS but found the inside very plain and simple so I wnet for the 2003 SSEi and so far very happy with the car.

The Northstar was upgraded in 2004 when used in the Bonneville with better piston rings and coated cylinders to eliminate cold slapping and rapping. My 03 Caddy STS was so noisy when it was cold and my 05 GXP is as quiet as the day it rolled off the showroom floor! The 5.3 does have D.O.D. which helps with gas mileage, but it'* not nearly as smooth.....in my opinion.