I gotta concur with the problem being the cam, rather than the journal. As you pointed out aluminium aint ever going to wear hardened steel - far more likely the cam's dodgy from the factory and has worn out the journal.

I'd be inclined to have someone weld & grind the cam into round, then find an appropriate sized bearing, grind the journal and slip the bearing in. You might even want to do ALL the journals while you're at it - that way it'll never happen again. Cam wears out? Oversized bearings (yay for old fashioned engineering).

Matt Electronic mods for TBA/SM!