273 4 bbl intake-plate riveted underside of manifold

As mention, they have a slight twist to their splines and will back out of you carefully use a small, sharp cold chisel on them. Tap the chisel lightly under the head of the rivet. work your way around and it will usually start to come out. It's there to keep hot oil from splashing up and hitting that hot exhaust crossover passageway. The old engine oils we had back then would burn and coke up on the manifold. This plate would (supposedly) keep that coke from building up and falling off into the lifter cavity. Good quality modern oils won't coke under normal temps, so, use it or not. I won't make much, if any, any difference.