[Walt Fricke]

Nothing I can think of which could melt due to use of a heat gun to loosen the cylinder head studs. Anything plastic is a long way from where this stuff was. Sounds like it was something which dropped in through the hole left by the engine oil thermostat's removal from the period of storage. Could be about anything.

Lead? Weber carbs have some passage ways sealed with round led balls as plugs. Don't know about Zeniths. Hard to imagine body lead getting in there. What else is lead in the engine or engine bay? Melted bearing lead isn't going to look like that, plus you said bearings look pretty good.

I've had the oil pressure sender apart. Little bits of solder for the little wires, nothing to amount to this. The idiot light sender has none, or at least even less.

Might be a good idea to pull the plug at the alternator end of the main oil gallery and see what might be in there, though.

If you decide to replace the plug with a screw thread plug, be very careful, as there is an oil passage at 90 degrees to the main gallery very close to the plug.