@dang2407 posted:Thanks panteradoug. Any thoughts on the viscosity?
I like 20-50 in a Cleveland. That was the original Ford recommendation for the Cleveland engine. It won't hurt others either but is a little thick to run in very cold climates.
The 289-302-351w are good with a 10-30 or 10-40. The 5w's are for the current engines. Don't go that thin with a high horsepower engine. The intent of it is to reduce internal friction and give the "fleet fuel average" better numbers but I think is too risky on the main bearings.
It wasn't unusual in the '60s for race engines to run strait 30 under race conditions. That isn't necessary here and you want "street engine" oil because of the detergents it contains.