The all stainless steel magazines were made for Model 645s. They were superseded by magazines with reddish orange followers. While both have feed reliably in my 45xx pistols the later magazines are of more interest.

At the time Model 4596s were made followers were yellow. 45xx series magazine bodies changed near the feed lips to resist the top cartridge being moved forward by the bottom of the slide passing over it. The change to black followers was to identify magazines with newer bodies. Since owners and sellers replace yellow followers with black ones you have to look at the indents in the sides of the body to know which they are. Cartridges feed reliably through both yellow and black follower vintage magazines in my 45xx pistols. The only malfunction has occurred during loading my 4506. The second cartridge has popped out of the feed lips of yellow follower magazines when the magazine is removed to replace the first cartridge that was just loaded into the chamber. Even that seldom happens.

Model 4596s are not common. I've only seen one. Hopefully my experience with 4 1/4" and 5" .45s also applies to to your 3 3/4" gun.