Dude that's awesome. I looked and yes,, the jack plate says CTS. I will have to go back to my garage and check the speaker frames. There are some numbers on the magnets: Under 16 Ohms, it says 137 7104. I know that's not what you mentioned but I left the garage for the day and that's the only pic I have on my phone. I didn't know to look at the mounting flange.
As an interesting back story, I am a Realtor and I have a client looking at homes. In a marketing photo of one of the homes I saw the Kustom cabinet and a Fender Bassman head in the basement. There was nothing else in the house. I scheduled a showing and out of frame was a 1976 Rhodes stage piano, a 2X15 Acoustic cabinet, a 370 Acoustic bass head, a Crumar keyboard I think from the early 80's and a cheap Crate combo bass amp. I bought everything for $400. I'm going to sell everything else to fund the restoration of the Bassman head and Kustom cabinet.