Thanks BERUSTY. My current header length is 5 1/2" which seems about right for the APC 11x7. I measure the header length the same way Mac's suggests doing it (see image).

Measuring from the glow plug, along the curve of the header, to the high point of the pipe is about 13 1/2" - 13 5/8" or so.

As you know, the 11x9 will definitely need a longer header length.

Looking forward to seeing the Calypso.

David