Well, I thought I might have a high speed detonation problem associated with the higher compression a/o S2 cam. Good news: the noise wasn't detonation. Bad news: the engine's torn-up for new connecting rod bushing! Wouldn't you know it - those were the only bearing surfaces I didn't address during the rebuild (just shoot me).
The bushings are available cheap (Thank God for Nigel), but can I replace them myself?