Gordon,
Appreciate the props for spelling the Queen's English the pukka way!
Do you know the history behind the difference? Apparently, the discoverer of aluminium, a Mr. Davy, actually proposed calling the element aluminum at first. Then in 1807 changed the name to aluminium to fit in with the naming convention for the other elements ending in -ium.
In fact aluminium was the correct term even in the USA until 1925, when the American Chemical Society decided to use only the aluminum name from then on in all their documents.
In any case, I am probably going to purchase a non-aluminum (sic) header frame as well at some point. Joe, I would be interested to hear whether you have any problems fitting it to your CMC.
Cheers,
Jim