I am sorry that this may sound like an advertisement, Honestly it isn't meant other than to let people know about a source.
I was referred to these people by a friend recently.http://www.generalradiator.com/
Mike is the main guy there and already has some info on core sizes for the MC9's as I am ordering mine from them.
He will call you back to keep in touch too... Great Customer service !!
I like when a business will return your call and check to see that everything is going well.