Gunsmiths - New England Pardner 12ga single shot

Anyone ever work on one of these before? I had a broken firing pin so I replaced it but now I'm having a problem getting the break lever aligned properly so I can hammer in the top sidepin. I can get it in with force, but when it's installed there is so much tension on the break lever that it won't move. The break lever worked fine before and firing pin I replaced is identical to the first. I'm following the schematic perfectly so I'm not sure what my problem is.

I took it into a local gunsmith and he doesn't know what to do either unless he files the hole on the lever but I'm weary of doing this since it functioned just fine before. Is there something I am over looking?