So... I contacted Carpy and he said his tri-bar light attaches the same way as a stock lens, with the same 3 prong bayonet fitting. Btw, he responded pretty quick... less than 15 hours after I emailed him!
But, OTOH, AnthonyMichael had issues with his Carpy light installation. So, I guess the answer is, it fits, but be prepared to do a few modifications if needed.