Here's another image from that site...

This is where it's clear to me that this started life as a pinfire rig -- note the right fence with the notch (most likely from a strike from broken hammer)

Also - the wrist of the gun pictured in the image I linked above here from the site is completely different, there's no stalking safety bolts on the locks, there's no group of express sights, the rib looks swamped from breech to muzzle...

Cheers
Tinker