Actually it wouldn't. I had a look this morning and the Cyclonus ears sit in a groove towards the bottom of the fuselage. So long as a new head occupies the same space roughly as the original "helmet" it will fill the space quite well. A Devcon head (with it's gun-looking thing on top) could even fill a hole that does pass right thru the fuselage with a Cyclonus head!
It is not a hole but a groove and I think its location would make it less noticeable than many imagine.
BUT.. my thoughts aint gonna make it happen anyway![]()