I guess that's understandable, thank you for that bit of history. I searched For awhile as well and could not find a thread size for the lens, the closest I got was one eBay auction where it was measured at the widest part of the lens, 1.625 inches, roughly 41 and some odd mm. Doesn't really help much at all sadly.
I hope you have luck with finding an adapter for it. I'll keep on looking for another 6x9 lens.