Removed my 4 bbl intake manifold as part of rebuild teardown. Looking at intake turned over, there is a riveted plate under where the carb mounts. One of the rivets has been replaced with a bolt. What function does this plate serve? How do you remove it for bead blasting, obviously the bolt can be removed but the one rivet is still in place. If I bead blast it, I'm concerned glass beads will remain trapped under it. Suggestions?