The Brazilian Navy S&W was a Model 1917. Some claim they were new made, but I have one, and have seen others, with U.S. inspection markings.
In any case, the thing inside the sideplate is a hammer block, the second type S&W used. The sloped surface on the hand contacted a right angle "lug" on the hammer block, pushing it out of the way as the hand came up. It worked OK except that it was its own spring and could easily break (as yours apparently did) or become dirty or gummed up an fail to function.
(It was that type of hammer block on the Victory model that failed and led to the adoption of the current hammer block system.)
AFAIK there is no source for those hammer blocks; Gun Parts Corp used to have some, but they are all gone. (P/N N53 in their catalog diagram.)
Now to the binding. The fact that it binds only when loaded suggests insufficient head space. First, give the chambers a good cleaning with a wire brush. Then, try different ammunition. (Try without the moon clips!)
If those things don't help, it could mean chamber(s) not cut deeply enough, or a replacement cylinder not properly fitted, or some other problems.
I would suggest trying to find a gunsmith who is familiar with revolvers (not easy) because trying to DIY could result in creating more problems than would be solved. Cylinder and Slide (
www.cylinder-slide.com) could do the job but they have a long waiting period and are expensive. I don't think S&W will work on those guns any more, as they have no parts, either.
Jim