'73 318 how do you know if original engine mount rubber is good?

This is the type where the rubber is inside a cylindrical sleeve. I have removed many parts for repairs and access to the engine mounts is good now. If the rubber is OK I would like to just reuse the existing ones. It seems the conventional wisdom is that rubber is better than polyurethane at reducing vibration. This is not a high horsepower hot rod and I want smoothness. Are factory style rubber replacements available?