Measure me a tripod ring...

So it worked well enough last time, when I was looking for a tripod-ring for my Samyang 35/1.4, turns out the 100L Macro ring fits it perfectly.

This time I've got another favour to ask, I need a tripod ring for my Medium Format Fisheye, the Zodiak 30mm f/3.5, so I can mount it directly on my P6 shift-adapter, swing the camera around the lens mount, and have a parallax-free fisheye-panorama.
Or something like that.

Anyway, the diameter of the lens barrel is pretty much 75mm, 12mm-wide where I can mount a tripod ring.
70-300L is 81mm, so that's too big, Samyang/100L Macro is 69mm, so that's too small.

Anyone with a 70-200 f/4 can measure the diameter of the lens at the tripod ring please?
Or the 180 Macro, MP-E 65, 200/2.8L? I'm not sure what else comes with a tripod ring, even a sigron lens tripod ring will do...

The 70-200 f/4 tripod collar is only 64-66mm, so that's too small for you.

The closest you can get from Canon is the Tripod Ring Mount B (in black or white), at 77-78mm. It fits the MP-E 65, 180L and the 70-200L (all versions)