Brad, 178 would be the patent use number; meaning that your action was the 178th made. It probably dates from about 1880. If it is the only number on the action, the rifle it was made into was of less than best quality so your action probably does not have much engraving on it. Thelever on the right side is indeed the safety, and does block the hammer. On most actions the lever can also be used to recock the action. Many actions from the same period as yours were made into the famous Gibbs- Metford target rifles. Jonathan Kirton in his book "The British Falling Block Rifle from 1865" does not list your action as a "recorded specimen" He does list action numbers 177 and 179. Most gibbs rifles of that perion were originaly chambered in .461 gibbs. Fewer than 1000 Gibbs Farquharson actions were made. You have a treasure, so treat it well.
All the best, Mal
