Brand new main bearing nicked. Usable?

In my opinion, I'd scrap ALL of those King bearings and get a set of Clevite or Federal tri metal bearings if possible. That little pit in that bi metal bearing isn't going to hurt anything if your hard pressed and have to use them, I just ain't impressed with those cheaper King bearings. They make a more expensive line of bearings,but I don't have any experience with those. Ran them in a 360 rebuild and in a couple Chevy circle track motors. Nothing but trouble. Replaced them with tri metal bearings and ran the **** outta them for years. Good luck with whatever you end up doing. Just my 2 cents bud

If the bearing quality is questionable like you say then I take back my comment, change them out for good ones I've used Clevite 77 bearings with good results. Come to think of it even factory bearings are tri-metal...? They definitely have a copper layer underneath the top layer, then steel.