Classic symptoms of a failed head gasket are bubbles in the coolant with motor running and cap off. Sweet smell of coolant in exhaust. If pump is good, flow should be good looking through the filler. Got time to do a compression check before you tear it down? I am sure it happens, but I don't recall hearing of an LC8 head gasket failure. Did you get it super hot?
My '07 has 35k miles on it. Runs good, no oil used. I won't even be thinking about a rebuild for a long time.
KTMs--300, 518, 990