I had the same dilemma but I didn't cut the panel I just purchased the Nav Console and sold the 4500 Radio along with the old console on ebay.
I am stereoless at present whilst I figure out what I want to do either install original ford stereo like the Ford 6000 or an aftermarket double din stereo.
You can get a ford 6000 with a Aux cable adaptor. I have bought the adaptor but I don't know which Ford 6000 to buy there seems to be 3 different sizes and even the smallest looks like it might overlap the console.
Ebay is the best option as Ford 6000 or 6006 new is £300-400.
Has anyone had any experience with this? Talking to some ebay sellers they say our Fiesta model is the pre-facelift model whatever that means?