The biggest risk/challenge with this job is that the bottom sweat fittings are very near to the stucco wall and side walk which was poured after the original piping work.
Anyway, worst case scenario is the you have to breaks some of that masonry.
The pressure regulator can be removed first with two wrenches . you should do that so it doesn’t act as a heat sink while you are trying to sweat apart the water valve. HOWEVER, first make sure that your water main valve actually stops the flow of water. You don’t want to break this open and find out it doesn’t, which is pretty common.
Definitely buy the mapp gas and a decent torch. Better to avoid putting too much heat than mess around not getting enough.
EDIT, Read B’s post, if that is drywall, not stucco, I guess you will just break it out and do a patch after. Use a piece of galvanized flashing as a heat shield for soldering, you can get one in the roofing dept. About 8×10 piece of metal that you can easily bend.
