What is the recommended oil for a Chevrolet 350?

If the engine is stock, you should follow the recommendation of the manufacturer. If the engine has been rebuilt or modified, consult the engine builder or use viscosity to maintain your desired oil pressure. I like to have 40 lbs.+ when cruising at highway speeds. I've run small block Chevys for many many years, and I've always used 10/30 oil,and never had trouble. later model 350's may say to run 5/30, that seems to be the trend. I go with what worked for me. (keep in mind I change oil and filter every 2000 miles, as we were taught in old school.)