Here's some photos to illustrate Pig Hunter's great instructions.
I used to have a box full of these I got dirt cheap somewhere. Sold most, gave away some. There is also a model for the 1911 which I've seen only one of. The holster was made Bucheimer or Bucheimer Clark depending on the year it was made.
You may notice the holster is the same as the one used in the early Dirty Harry movies. It has the narrow retention strap and a tension screw like one in the movies.
I used to make the harness to replace the elastic harnesses found on most vertical holsters. Haven't made them in years. I replaced the leather lace with Chicago screws giving the harness more flex. I also used heavier leather and wider shoulder straps to carry the weight of a larger frame revolver better.
You might want to replace the laces since they are the first to fail.
I think once you get the holster adjusted you'll find it one of the most comfortable holsters around.