"Unusual" translates to seldom (if ever) seen. Throughout the years, one could order a target sighted gun with any available front blade. Very few buyers did so. Quite a few owners changed or otherwise messed with their sights, but after the fact of becoming owners.
Ralph Tremaine
Same church----entirely different pew: There were two different "Olympic" chambers. I refer to them as "short", and "really short"---the latter being the earlier version. My earlier version is on #10617---the later on #11112. If perchance you have one of each, it's a simple matter to determine which is which. Drop an identical cartridge into each (SQUEAKY CLEAN) chamber-----only as far as it will go with NO pressure. That which sticks out further is the earlier version. The difference between the two is .025" (+/-). I'd ask which you have, and the serial numbers for each gun, but I've been there and done that---only to learn the change was not made "in order". As an aside, there is no measurable difference in the accuracy provided by these two different short throat pistols.
I really like these old target pistols ,I am not at a point that I could afford a sure enough collection but they sure are cool ,thanks for posting and thanks to the walking encyclopedias on things target for educating the rest of us.