I'm holding a cut-off/shortened basketweave Heiser 510 on a 61 drop loop belt for a friend until I can send it along to him. Besides the crude shortening, it's notable for having a thong instead of a the safety strap (stitch holes visible) and a cut-out to clear an adjustable rear sight. Antique good condition or thereabouts.
A couple of days after packing the holster back in the box, I browsed the 'net, bounced around FB and then hit upon the page for a man identifying himself as an archivist at Colt. How cool is that?
I scrolled down his page enjoying pictures of a variety of very nice Colt handguns when I noticed one and then two pictures of a Colt Official Police with a shortened Mexican Loop holster on a drop loop Buscadero belt. I gave those a brief look and went on ... and then went back. I opened the pictures to full page and then copied them to blow them up more....
Same holster. Every detail matched, including the basket stamp and stitch count. The OP was identified in the pictured factory letter as having been shipped to Major John Irving whose name was factory engraved on the sideplate. The date is partially covered but might be 1937.
Thinking there might be a story there, I pm'ed the archivist who replied that he had owned both the holster and the revolver - but they were not a set. He'd bought and sold the holster separately. Still, I was tickled at the discovery. What are the odds?
I neglected to ask permission to post his pictures, so you'll have to take my word on the match.