Pop a bearing out of a rod or main cap, they're stamped on the back, .010, .020, etc. Your heads are too old to have hardened seats. They won't last real long on unleaded fuel. I've had them go 30K miles before they pound out, though. The ones you have aren't worth the expense of installing inserts, and I don't have much luck with them, anyway. Find a newer set that are factory hardened.