Pretty hard for me to help If you can't get the set screw out, not sure what it looks like. I'm a retired mechanic, I've always been able to get things apart but sometimes it's not pretty! Set screw are usually to hard to drill, I have an impact driver that works sometimes, and sometimes you just have to grind it away. A torch might work, but it needs to be a hot one like and acetylene. Have you tried googling the disassembly procedure for your valve? There are a lot of good videos available. Maybe someone with more experience with your particular valve can give you some better advise, good luck!