nut down the manifold
i would be very concerned. the manifold delivers the fuel/air right to the engine's cylinders.
if you are sure that is where it went i would be taking the manifold off and looking into head area and i would be shaking the manifold hoping it would fall out.
i don't know how the rest of the guys would treat this but to me it would be defcon 4 and i would not even attempt to start the engine until i was sure it did not get to a cylinder head. even if it couldn't get by the valves if it would catch there and not let the valve close smack on a pistion is possible.
1972 350sl Red/Blk 117k
1988 420sel charcoal/Blk 140k
1987 420sel gold/tan 128k
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Pound it to fit then Paint it to match!
There is only First Place and Varying degrees of last!
Old age and deceit will overcome Youth and Enthusiasm every time!
Putting the square peg in the round hole is not hard... IF you do it fast enough!
Old enough to know better but stupid enough to do it anyway!