I seem to recall that everyone thought you could, but not sure that was the case in the real world. I owned a Python back in the early 90s at the same time I carried an issue 686 for a while. I know I had speed loaders, but I don't remember if I had a set for each or used the same ones for both guns. I rummaged thru a box and found two Safarilands I used. They have no markings other than "GL8C," and I know I used them for duty with the 686 for a while because they still had Southwest Border dust in them. I never carried the Python. I remember looking for speed loaders on weekend breaks from the Border Patrol Academy, but couldn't find any in stock. I know I had a set by the time I reported for duty, but don't remember if I used the ones I had for the Python or found some along the way. Best way for you to see is what works is to break out what you have and try them.
My experience with Safariland speed loaders was not good while I was a Border Patrol agent. I found that when they got choked full of dust, they wouldn't release. I ended up switching to a Glock 17 and turned in the 686. Later, I carried a Model 19 for a while, but because of the dust issues, I used HKS, which seemed to work regardless of how much kicked up dust I had to work in. The Safarilands are very fast for competition; although I recall seeing an agent on the Border Patrol pistol team back in the early 90s competing in a weekend law enforcement match in San Diego with his Model 66 and his duty rig. He used HKS speed loaders as I recall, and reloaded so much faster than many of the other competitors did with semi autos.