Malamute,
I certainly understand your concerns. However. Your not going to find an "Idiot Proof" Open Top. When Abilene mentions the "early" Open Tops being chambered in 44 Russian, we are talking about around 15 years ago. Your chances are better at winning the lottery. For the most part, the more current build of .44 Open Top, regardless of markings, are chambered for 44 Special. It's a cost effectiveness thing. A single set of chambering cutters and finish reamers. One size fits all. Although in the past, there have also been some Open Tops marked 44 Colt that would not accept 44 Special cartridges.
If your primary concern is someone, in the future "may" stuff a 44 Special case, loaded to 44 Mag performance in your old Open Top, then I would suggest you pass on the acquisition of an Open Top. Similarly, your 45 ammunition is only safe in an Original Ruger. Understanding, once your unavailable to shout "don't do that" someone may well stuff one or more of your 45 cartridges in a Colt or a Reproduction there of, and blow it to smithereens.
Navy 45, we're a lighthouse, Your Call (Navy 45 demanded the approaching lights "change course" while refusing to change theirs.
Coffinmaker