Hi Philip
I myself did not do the work on my lock. But the guy who did explained it to me. Driving that pin out and the rest of the lock will easily dis-assemble. As I recall, the tumbler and shaft are one piece. So the tumbler/shaft and hammer are all held together with that single pin. The original Portuguese locks are built the same. You might remove the mainspring to allow the hammer to move freely to give you more room to work (?)
As I recall, Forum member Sam squanch (above) used one of these locks to make a pistol. He might also provide some hints.
Yes, your lock is likely never been used. Most of these locks you encounter today were from that original Dixie Gun Works inventory back in the 1960's and 70's. Notice no holes were drilled in the lock plates - which in our case was good. LOL
Rick