1968 ( 318 ) main bearings - Input requested

Just my thinking on this subject; a lot of this is just thinking out loud. A lot of the King bearings are aluminum of some sort. IIRC< the King;s for the SBM's are AL. Supposedly harder, so the bearings are more wear resistant and have looked good in my stuff when removed.

I have raced on Al bearings in my turbo rally engine; that engine (late 2.6L Mitsubishi) has a much better oiling system design than some of the SBM stuff.....(just my opinion on that). But since you are pushing higher RPM's and loads in your SEGA engine, then I'd be thinking more about crank oiling limitations, and would push towards a softer bearing surface than AL.... just to give things their best chance to live in case of a slight loss of oil for a moment.