I think the baffle is a shield to keep oil from splashing onto the under-side of the manifold. The V-8 intake manifolds have carburetor heat passages in them. Oil splashing around there would soon form a heavy layer of carbon. I think the push-pins are actually rivets. I don't see why self-tapping screws with thread locker wouldn't be satisfactory to hold the shield in place. If the rivets are in pretty good shape, you could probably flatten the shank a little, then drive them back in. But, I don't know how durable that method would be.

Harvester