Merry Christmas all!

I've got this old Stevens Mod 311 - Series H double barrel 12 gage shotgun:






My son was using it when the right hand side ceased firing. As it turns out the sintered metal hammer broke at the pivot hole.

I've got a replacement hammer and am trying to install without any luck. Before I damage either myself or the gun, I was wondering if there are any pointers for installing the hammer? A bit of spelunking around the site seems to indicate that it is a challenge without any real advice (other than making a special tool) on how to install the hammer.

Can someone please provide words of wisdom?

Thanks

Chris