Use carb cleaner and see if it will rub off. If it does, it's varnish. You can remove varnish if you use the right cleaner and a decent cloth.
Then, check the bearing clearances with Plastigage and if they're in spec put it back together and run it.
It sounds to me like this car sat a LOT and the engine oil got wet and degraded. You need to check all the wear points.

You're going to get all sorts of replies that tell you to go expensive, replace rings, bearings, grind crank, etc. It's easier to throw parts at a motor than to figure out what absolutely needs to be replaced.

Measure everything that you can.
R.