That's some beautiful machine work!
Will this be a shooter?
I don't know what the steps are called, but they're there for a reason. You set a handspike across the step in the cheek, with the end under the tube, to raise the breech of the gun and adjust the quoin.
The multiple steps give you a better range of adjustment.
Smaller guns could possibly be wrassled up by hand, but raising the breech on a 24-pounder is going to require some leverage.