It is my understanding that these parts were "sort of" hand fitted in two ways. First, the double action sear, which is the little lever on the front of the hammer, was actually fitted. Both length and shape of the double action sear are pretty sensitive. Second, the hammer and trigger may not have been hand fitted, but the assemblers had bins full of each, and if they did not like the way two parts fit together, they would swap one or the other. Since overall dimensions on these parts had a few thousandths of variation, swapping parts could result in a very good overall fitting. Of course, some assemblers were better at this process than others, and we can still feel the results of that when we handle older guns.
Regarding swapping parts between guns, it might work out fine, and if you are well experienced working on revolvers, it would not hurt to try. Since you will be keeping the same hammers and triggers paired up, there is a good chance that the double action sears will be fine. I would suggest keeping the hands in their original guns. This will require removing the hand from each trigger and installing it in the other trigger.
If you do try swapping parts, and things don't feel right, then I would recommend putting everything back or talking to an experience gunsmith. If fitting is required, it takes some real experience to do it right.
