Many different companies used similar trigger return springs that look like the one in your H&R. Iver Johnson used that same style on some of their top breaks, but the metal on the IJs are a bit thinner and also a bit shorter. U.S. Revolver Co. (also made by Iver Johnson) pistols used them too. It might just be that it is a different manufactures trigger return spring and that's why it doesn't fit correctly.

And yes, I agree with Les B. about the firing pin.