You can try cocking the hammer and then gripping the portion of the pin which protrudes out the back with a pair of vise-grip pliers. This will allow you to get the lock apart and then after marking the pin you take a wadded up cloth in your hand and put it over the pin and spring then release the pliers allowing the pin and spring to jump into the cloth without getting lost or hurting you. You then drill a small hole through the pin at the point you marked so that on reassembly you can push a paperclip or similar piece of wire through to hold it in position while you assemble the rest. I haven't done this on a Spanish lock, but it does work for a Great Plains lock.
