I have seen this problem numerous times on twin cams, of course 90 percent of them are from installing new cam (the more radical the worst) without replacing the inner cam bearings with full compliment bearings, or worst, not replacing the bearings at all.
The worst I have seen actually siezed the engine up. Tore up the pistons and bore of the cyliners, clogged up the oil pump, seized up a liflter by wedging a roller between the lifter and case and welding itself there.
Even in this instance, the only reason I replaced his cases also was because the outer bore for the bearing was so far gone gone, and egg shaped that we couldnt do anything with it. Just made it an expensive paper weight. Usually bores can be repaired and parts can be replaced, and case halves dont have to be replaced.
In all of them the same thing happens, fist is the tinging, like a small chain in the engine, or cam chest. Then, comes the suffering performance of the bike, then comes the infamous seized engine. And all this can take time to develop, or just moments.
I recomend splitting the cases, inspecting every inch of the engine, repairing and replacing as you go. remember your bike is no good broken down.