Any SAE aprroved motor oil is fine. Ususally I run 15W30 in a 350 unless I am in a really hot climate. Then I would use 15W40. All SAE oils found at any auto parts store meet or exceed manufacturers specifications. I personally like Valvoline.
A/c delco.
10w30 or 10w40 should work fine in most climates.
1976 Chevy 350 engine should take 5 qts engine oil with filter change.
10w30 or 10w40 should work fine in most climates.
10w30
10W30 would be recommended.
10w30 Detergent oil from any major brand will work well.
Mobil 1 synthetic.
A/C delco
10/30 or 10/40 should be fine. You could use a heavier oil such as 15/40, 20/50, or straight 30 to increase oil pressure.
lucas oil
depends on the type of oil pan being used, but most were 5 or 6 quarts.