Any upgraded stereos in 348 Spider?

What size are the speakers in the doors ?, I have 5 1/2 round Focals I wanted to install them, they also came with a nice tweeter, How hard would it be to install this tweeter where the old ones are ?
Any Help would be appreciated, I just bought my 348 Spider and the dealer did say the stereo wasn't working so this is a top priority when it arrives

 

My door speakers are AVI 6.5 inchers. I can't tell you how hard the install was because I had it professionally done. But it doesn't look like they had to do any kind of surgery on the door and the installer didn't mention any particular problems except for the general lack of space and access. Also, the 6.5 inch speaker matches the cutout of the door panel.

The tweeter should be easy to install. Once you pull the side A/C vents off (directions can be found here if you search, but mainly be sure that you don't break off the tabs that hold the vent in place) you'll see that there's a lot of space behind there to add new hardware. And it's behind the grill so the install doesn't have to be very pretty.

 

Can you post the model numbers of your system?