OP, glad you are getting good results with your model 64. There is a lot of good stuff in this thread, and there are a couple of things I want to respond to. I am sorry I missed this thread when it was first active a couple of weeks ago.
Earlier, there was discussion about whether .357 magnum revolvers need greater mainspring tension. Well, the S&W armorer's manual says that they do. In the second post of
this thread there is a page from the armorer's manual. In the center top of the page it specifies that the hammer should support 3.25 lbs on a .38 special and 3.5 lbs on a .357. These weights of spring tension are the S&W spec which is intended to be reliable with all factory primers. The issue is that some .357 ammo uses magnum primers, and some magnum primers are harder than small pistol primers. Obviously, if you reload and you use the same primers for both types of ammo, then there is no difference. But if you want to use all types of factory ammo, then greater tension is recommended for .357.
The image in the thread above also shows how to measure the tension on the mainspring with a trigger gauge. This method can make the process of adjusting spring tension much more scientific.
To the OP, I wrote a long article about working with S&W revolver triggers that is intended for people who are getting started with these projects. You are clearly past the beginning point, but I will still offer a link to the article. The article is here:
Improving the trigger on Smith & Wesson Revolvers
And it is also discussed in this thread:
https://thefiringline.com/forums/showthread.php?t=584772
Good luck with your revolver. You have started down a road which I personally have found quite rewarding.