Dillon's manual for the 650 says the mounting surface needs to be at least 14" deep, but there are some things to keep in mind.
First, when mounted, the 650 hangs over the front by several inches. Second, the 650 doesn't come with a case feeder and it's not clear whether the 14" is sufficently deep for the optional case feeder. Third, the top of the bench needs to overhang the front of the bench by at least 3/4" to allow clearance for the handle and linkage.
It doesn't sound to me like the 650 will work well in the space you have available. Even with a 14" deep bench, the front of the press will extend further into the garage than the garage door tracks.
If you want to go with 14" deep and don't mind the slight intrusion of the press beyond the tracks, I'd call Dillon to verify the 14" requirement is sufficient for use with the case feeder.