Thanks Brian - hmm "preset", so not the one with the aperture plunger, eh? Maybe not so common on the great auction site in the clouds (thinks: must set a search).
I have a 39mm 28mm lens somewhere - I have a feeling it's off a russky 1/2 frame, so probably not enough releif to get it shimmed for ltm - unless you know different.......... [manic laughter]