Evilokc, I would try pulling the spark plugs ,and valve covers, and get an inspection camera
they are about $50 on craiglist around here new and see if it made it in the cylinder:
https://dallas.craigslist.org/ndf/tls/6210069027.html
I would NOT fire the engine up with it in there, if it is a stuck valve, can bend it break it damage the piston and cylinder wall.
If you cant locate it by looking in the cylinder , may be able to tell by the looseness of the push rod .
If it didn't make it into a cylinder, also check the push rod for that valve for being bent.
But regardless you're just determining where to go fishing for it , odds are you'll have to pull the head. I don't know if your engine was a recent build, if it was may just want to pull the one head, if not maybe pull both and go thru them and have them both freshened up.