As the factory-replacement-part hammer comes from the factory will be significantly TOO LONG if you get one from the factory.
It must be shortened, and a clearance angle applied to the leading edge.
If you can compare it to an existing hammer assembly, you should have very little difficulty.
The method you use to shorten the double-action sear, is up to you. I used a needle file, and without removing the sear from the hammer.
It took longer than I cared for.
By the time I was done, I wished I had knocked the pin out, and worked on the sear without it being still installed on the hammer.
Now, here is a picture indicating the single action notch.
Look where the red arrow is pointing.
Not too bad a picture eh?
If there were something there - like a NOTCH - you should be able to see it, right?
Look at the vertical greasy line.
There is a "bump" there, that constitutes the single-action notch.
See what I mean when I say messing with the SA notch is not for amateurs?
I didn't mess with the single-action notch, and I discovered that the factory-configured notch (such that it is) works just fine in single action mode. If somebody ever was to get charged-up to work on that single-action bump, they better have a Mark IV eyeball, a steadier hand than mine, and a powerful microscope.
Here is a DAO hammer assembly.
Notice the complete absence of a SA notch.
In closing, let me relate this piece of information. I was AMAZED when the folks at Smith and Wesson told me they have ZERO replacement firing pin nose rivets for sale to yahoos like me. If you ever want to replace a busted firing pin nose (A.K.A. "firing pin"), you gotta knock out the rivet on the hammer to get the busted nose out. I bet Smith and Wesson has a stash of rivets, but they must be short, 'cause they sure wouldn't sell me one. I finally found some for sale in Canada on the internet at
http://www.marstar.ca/swrevolvers.htm
I ordered three.
They sent me three USED rivets.
Funny no mention of "used condition" on the web site.
If you want a SA/DA hammer for a Model 64-5, you better order one tomorrow, 'cause I'm reckoning they gonna be "short" on those little jewels right soon.
There it is. The story of converting a DAO Model 64-5 to SA/DA.