Here’s the reply from Celestion:
Hi Vaughn - it’s a custom special, and a prototype sample at that, so I'm not really at liberty to give you any detailed info.
However, from a brief look, it's got a 35oz magnet, so a little bit different from a Vintage 30 in at least that regard.
Regards,
The Doc
Dr. Decibel, Celestion
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So it’s got the same size magnet as a gt-75. The front of the speaker appears to be vintage 30, at least the dust cap size. It is rated at 240 watts(on the cabinet tag, at least). So maybe a V30 type speaker with a 75 magnet? Sound wise, I’ve always thought it was smoother than a V30, less mid spike. My other cabs with V30’s are 8 ohm cabs and I don’t have another 4x12 fully loaded with V30’s to compare to.