Neat and welcome Mike. I was a Teaching Assistant to a Dr Breitenback in the Dept. of Zoology at the U. of Mo. - Columbia in 1973-74. Any kin?
1. When the gun is cocked the pins are free floating and should move freely. The left pin may be gunked up. 2. ANY 100 year old gun needs a good check and clean and the head of the stock examined for cracks. 3. Be aware that the original chambers were 2 1/2". If they are now 2 3/4", a very careful measurement of the wall thickness at the end of the chambers is critical. You should NOT use off the shelf 2 3/4" shells in the gun if the chambers are 2 1/2", and I would advise against lengthening the chambers.