Found, One from fellow member, one popped up on Numrich!
These are my most often carried firearms and I've decided if I'm going to keep them and use them this much, I want them like I want them.
I know a hammer from a 4506 will work in the 4516, and Numrich is out. That and I'd hope a used hammer would be less expensive.
As far as the 6904, I think a 5906 would work. I've read that they all will interchange, by keeping the current stirrup (changing it over). I'm okay with any color. PM me and let me know what you have and what you want for it (them).
Thanks!