Advice on replacing 12 in woofer in Martin Logan Monolith III's

You would think this  measurement would be on the Internet. I've looked at MartinLogan site and around the net, but can't find it. 

No it's not, as I found. You'll just have to do it yourself as I did, wish I saved it all those years ago.

Cheers George

Steve, here is Jo Fo's front speakers, as you can see his centre something his subs are not in the picture.
http://www.jonathanfoulkes.com/images/Animation%20FullFrontViewFlipBook.gif

Cheers George 

With a lot of advice and help from Tim (Timlub) I purchased a Dayton 12 inch driver. Since I'm running a dbx 260 active xover, I was able to to dial in the xover points and the slope,  it sounds amazing.  Also I added a SVS sub, which really brought out the lows.  Still have some room EQ I need to deal with, but overall it sounds awesome. Thanks Tim!