Good point. Most of those Spanish guns used an underlug that was silver soldered onto the bottom of the bbl. First make sure it's not loaded. Then you remove ramrod, tang screw and drive out the pins holding the fore-end to the bbl and then turn the gun upside down (muzzle down and with lock area at waist level). Tap the muzzle against you shoe and this should help "pop" the stock off from the bbl. Have a hand in position to catch the bbl when it pops off. This method avoids "peeling" or lifting the bbl off as you can damage the stock. Check the bbl to see if the underlugs are silver soldered on. If they are, the concern raised by swampsniper is moot. If the underlugs are inserted via dovetail cuts, look at the hole to see that it is in the underlug and not into the bbl. If it's in the bbl, shine a line into the hole and look through the muzzle to see if there's any light showing through.
My benchmate at my last class drilled through his bbl. :banghead: Our entire class was visited by the Gun Gremlin who made his home there.