What is the recommend oil grade for 1977 350?

Answer 1

It's less about the year than it is about the condition. As the engine wears you'll need a heavier grade oil (higher numbers). If the engine is new and the bearings are in good condition use an oil with lower numbers (5W15 or 10W30) and when the engine gets a little "tired) start using heavier grade oils such as 10W40 or even 15W50.

The rule of thumb is, watch the oil gauge. If the gauge starts going down too low or if the oil pressure light starts coming on when the engine is at an idle, switch to a heavier grade oil.