A little update:
I bought a 150/9 Germinar-W in the first round, and it's been sitting here since. My spare #0 shutter was "dodgy", and the one which was good had already got a 121mm Leitmeyr Weitwinkel-Anastigmat in it. So the Germinar was left out.
Then about a month ago I bought a Zeiss-Ikon shutter for the stunning price of about $7.50 - it probably came off a folding camera. It was here waiting for me when I got home from the North Sea.
And today I got the brilliant idea to see if the Germinar cells would fit in that shutter.
They did. Spacing is correct too, at least to within 1/20 mm, which is as good as I can measure.
Aperture markings also seem to be exactly one stop out, so it seems the shutter has originally held a 105mm f:4.5 lens in a 6x9 camera.
Maybe it's time for another "normal lens shootout"? 135mm Eurynar, Planar and Skopar; 150mm Germinar, Tessar, APO-Lanthar and Heliar; ca. 150mm Aplanat, 6" Serrac?