They are recommending replacing 2 of my vintage 30's in a 4X12 with one of their blue dog ceramic 12" and one of their silver bell ceramic 12" in the 1/3 positions.
I bought a 30W 12" alnico Blue Dog, when I found that my existing speakers didn't give my AC30CC head justice. It was between two 15W celestion blues ($600 a pair, if your lucky) or the 30W weber blue dog ($170).
THe price was a no-brainer. I did a bit of research and posted some request for opinions about the blue dogs. Blue dogs seemed to be the best replacement for Celestion blues.