Well, I made a mistake. If I read correctly the M-18000-ZX3B dampers while spec'ed for 06-07 focus should fit on the 08-11 focus. What I did wrong, was I bought the 08-11 (H&R P/N 51662) springs. In this spring set the front springs go down to a 4" coil on both ends, but the M-18000-ZX3B front struts have pockets spaced for ~6" coils on both ends. To fix this I believe that I should return the H&R P/N 51662 and go with H&R P/N 51666 that is made for the 06-07 focus.
Even with this fix, I haven't been able to find any data about how the H&R spring rates compare to the M-5560-ZX3B springs that have been discontinued but I'll find out when I drive it. Ahh, details...
Seat (strut seat similar)