What’s best to use on cast aluminum valve cover. I have to close off 3 sides of a baffle. Don’t want what ever I use to fall off. Thanx.

Myself I would redo the baffle but the stick would be thicker and stay where you put it and metal prep would be key on all.Do you want to use an oil restrictor in the heads ?

If you are adding the entire side I would make flanges and mechanically attach it with rivets, or screws. If its to seal it up at seams, I have used J-B on aluminum with success for sealing oil, but not successfully when trying to attach something in there.

I made some baffles out of flat a thin sheet aluminum and had them welded in, the welds broke but the baffles stuck in the valve covers and haven't drop down onto the rockers yet