Thanks all. I had seen the earlier post kayakamina but Aperio's post caused me to reconsider.
Also, Collins Dictionary which MM sometimes uses defines gyron as "a variant spelling of giron".
For some strange reason, Chambers online at:
http://www.chambersharrap.co.uk/chambers/featu res/chref/chref.py/main
fails to bring up a definition of either spelling, which complicated matters further until I checked in my book version of the dictionary.
All the same, as you say JimJools, they should accept either.
Thanks again.