Make sure to double check and see that it is not back upstream in the intake manifold somewhere. Stranger things have happened. Would suck if it was and you didn't catch it goin back.
we had this happen with our hemis what "chrysler" was making the cylinder heads awhile back... the seats would fall out and then all hell broke loose...
well one cyl eat some valves then shoved the rest of the valve thru the intake into another couple of cylinders...