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Is it possible you're confusing them with the 4550bka? See http://www.jblpro.com/pub/obsolete/Low_Frequency_Enclosures1.pdf

BTW I'm still looking for plans :)

http://www.ric.hi-ho.ne.jp/audio/image/2005%2001%2030jbl4550%20021.jpg is a good example of essentially the same thing. As was already mentioned, google image search is your friend.

Also, I'm...