Do you have the Sunn 4-12 square cabinet or the 4-12 coulmn?
The square "guitar" cabinet will take most any 8 ohm 12" guitar speaker...many of which sound better then the originals.
The column, however, takes a special 12" driver, no lomger available from Eminence...but I do have to have a few of these on hand!
e-mail me at loizcren@erols.com if you want more info.
Tom