Paul, the idea behind Osgear ends was simply that you did not pull the wheel over, we were all using wingnuts then. I had the osgear ends on my 1951 Les Vince, I stuck a pic of it on here somewhere.
The real thing can be found here:http://www.classiclightweights.co.uk/de ... ar-hs.html
H Stone does say that the early Margherita gears had a sprung tension arm, they didn't.
The pro Osgear had an additional ratchet control on the side of the gear lever to de-tension the sprung arm. Pros in the 30/40s were very fussy about keeping the chain slack, hence the revised Simplex with 2 cables, the Paris/Roubaix which slackened the chain as you tightened the wheel, and the design of the original Gran Sport tension cage spacing, to run freely.