The most popular product is aerospace 303,but thats only good if you have a lot if plastic covers.

On a old engine with no plastics maybe a engine bay laquer like swissvax motorshine would work okay on rubber hoses ect

To clean your bay you need some g101 or some kind of apc spray everyware agitate with a brush then rinse off with a hose pipe,if its bad you might need a stronger degreaser.