So, I've disassembled and reassemble the transmission several more times. I've tried unflipping the clutch, tried using the shim I found in the bottom of the case, and performed (poorly) a few incantations from the Necronomicon, and that cocksucker just sits there. The rear wheel will spin lazily at idle on the centerstand, but if you rev the engine all the way up, an infant can still stop the wheel with his bare hand.
Come on, fellas. Somebody gotta know somethin'.