You'll need an HD ACM and Forscan to modify some settings with your car. I added an HD radio to my 17' and got it off eBay for about $80. It came out of a 16' model Taurus.
I found that an ACM out of a 11' - 15' Explorer / Taurus will bolt and plug up. However, the CD slot of the ACM will not line up correctly with the slot in the faceplate around the 16'+ Explorers. Everything else will work, but the CD won't make it into the ACM. If you don't need the CD function, you could possible pick up an older ACM even cheaper. If you need the CD function, look for a 16'+ ACM.
When on eBay, try to find an ACM that has a picture of the big label on the back of the unit. An easy way to tell if it's an HD unit is to look under the barcode for the SDARS EIN #. In this space, it will have some fine print talking about the HD copyright, etc. On a non HD ACM, this space is just blank. This will be right above the "Made in China" Clarion info.
I'm sure there is a way to figure out what Ford part numbers are HD or not, but I didn't spend that much time on it to figure it out.