this thread has really got me wondering. backfires are pretty rare, but I can't say never. my bike was built in november of 04 (05 model), so it is in the problem range.
I am thinking that at the end of summer oil change that it might be worth the cost of a clutch cover gasket to pre-emptively press a steel bushing over both of the possibly suspect parts. From the pictures posted, there should be plenty of room to get some reinforcement in there. Has any body done this?

05 speedmaster - 1100cc, 11:1 racing pistons, Carillo rods, thunderbike cams, ported and polished head, 2mm over intake and exhaust valves, Barnett kevlar clutch, scepter pipes, oversize manifolds, 45mm HSR's, TTP stage 4 firestarter