riff said:
Do the speakers screw directly into the grill or is there some sort of T nuts w/bolts?
The speakers are rear-mounted. There are machine screws mounted through the cabinet's front panel, with the threads exposed on the inside of the cab. Just shine a flashlight into the back of your combo, you'll see the locking hex/acorn-style nuts holding the C90's to the cabinet from behind the speaker frames. On my amp, these screws aren't long enough (or probably heavy-duty enough) to fit all the way through and hold the heavy frame of my old EV -- maybe yours will work as-is, but I doubt it.
Anyway, you'll have to take the whole combo apart, I think... rear cabinet panels, amp chassis, reverb pan, everything has to come out before you can access the speaker mounts. I believe once you get everything obvious out, the last thing will be to remove the decorative front panel, which I think is screwed in from behind the cab front with 4 little screws in the corners. Then you can get at the speaker mounting screws from the front. Some good news is that once you replace the mounting screws, you can leave the new ones in even if you want to go back to the C90s or anything else.