I've had this rifle for many years and have finally decided to do something with it.  It has the rimfire FP but not the center fire FP which looks like it was held in place with a threaded bushing which is also missing.  Normally, I would try to replicate original type parts but would really like to see what they looked like.  I can't find any images of this set up just the later centerfire only firing pins.  Then I think maybe I should just modify the breech block(s) to use a cross pin to captivate the FP.  Is there anybody here who can help with images of the original set up?
Thanks for any replies!

Thank you for the reply!
The rifle was made by Brown Mfg in Newburyport MA.  According to Flaydermans it was only offered in .46rf by Brown Mfg as you note.  The last three digits of the sn on the breech block(s) matches that on the frame and the work on the breech block(s) and hammer look factory done - certainly by somebody who knew what he was doing.  The sn 21XXX indicates the very end of rifles made by Brown.  A cross pin or set screw to captivate the FP would have a much simpler method than what was done. I'll post some pictures when I take it apart again.