Unless he is having a very, very slow day it is unlikely in the extreme this would be a while-you-wait job. The trick is not so much getting the old one off as getting the new one on. It is unlikely in the extreme that the new one would line up properly, so it would probably need to have the shoulder turned down, and it might then need to have the barrel/cylinder gap re-set or the forcing cone squared. This can all be done with hand tools, even setting the shoulder back, if you have some good files and are REALLY slow and careful. I have done this on medium and large frame steel guns. I would never never ever try it myself on a j-frame. Way too easy to tweak it. You would need at a minimum a frame wrench, which you can make one of yourself with some time and angle iron and a barrel clamp, which you can make with some good hard wood a router and a lot of patience. It's still a bad idea, pay a pro to do it. Then you've got someone to come back on if it turns to crap.
