I would ask the lab. If the head was intact, then they might take it despite being separated.
Honestly, the upside down thing is not really that bad. Sick birds just kind of go to sleep. I walk them slowly to the place, talking calmly to them. Usually telling them how much they were loved, cared about, and what a good bird they are, thanking them for everything, all the eggs, etc. Makes ME feel a little better anyway. Slowly turn them upside down, everything slow and deliberate and calm. If something is off, just start over, take your time. Wait until they are calm (they don't usually get real worked up), and just proceed. It is usually fairly undramatic. Make sure the blades are positioned correctly, do it, and walk away if needed and breathe. I have never messed one up this way. I'm not going to say it's pleasant to do, but it's far better than some of the other ways. And early on I did have some screw ups doing it other ways, and it was horribly upsetting. Honestly, the best way to do it, is the way you are personally comfortable with.
I only have one Wyandotte left, lost all my others to Marek's. I have one old roo left that has never shown symptoms. My brahma's also seemed very susceptible to Marek's, have only one hen left.
