I got me a barrel 210 Heliar a couple of years ago. After some time with a Sinar shutter, I wanted something a bit more quiet and by coincidence found a Schneider Xenar 210/4.5 in a nice working Compound #3 at around $100 on the german feebay. (The very same combo which Ole speaks about.) As Ole says, just swap the back and front elements and you have a shutter with a calibrated aperture scale. Both lenses comes from the between -39 and -42. As your lens is a barrel lens, I can imagine that it holds some vintage too.
While these Compounds may not be the most exact shutters by todays standards, they look and not least
sound beautiful. Especially when used at longer times where there is no "whirr", just a soft silent "click .... click". Besides, any good camera technician should be able to CLA this shutter.
I havn't done any side to side testing yet, but I doubt there will be any difference between the lenses, except when fully open, where the Heliar has its very original signature. (The Xenar should also be nice fully open, but not the same as the Heliar.)
Last, congratulations on your latest little piece of "holy glass"

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//Björn