Lindsay 1863 superimposed rifle musket?

[thatoneguy82]

I am jn the process of acquiring a Lindsay 1863 two shot musket that's been cut down and is missing the lock assembly, I'd like to make a replacement but I'm having a hard time getting any info on the layout of the internals. I'm particularly stuck on the self selector trigger/ sear setup. Does anyone here have any insight into these monsters?