The antenna for the GPS Speedo is probably going under the center speaker grill somewhere. I put a GPS radio in my 06 Charger Daytona back in 06 and left the GPS antenna on top of the radio in the dash and it works perfectly.
Dash cluster is still a little crude, but it works. Will have to deal with the blinker lights and such also. The different angles make it very difficult. I didn't do it personally. It is still in the shop doing the mock up, so I don't have anything more than this. I know he had to shave the back of each hole to make them flat. Not even sure how he did it, but it looks like I wanted it to so