Talked to Eckler's today. The 21" dimensions for each speaker section are correct with an adaptable 14" center section but it's meant to fit up high which provides about an extra 18-20" of available space. I had measured available space flat on the deck, silly me.
I went ahead and ordered one 'cause I want the Vette "complete" by the end of March.
Ought to be able to offer a reasonable T & E for ya Larry, just give me a bit of time.
Ken