Having a big ars strap wrench usually pops the forearm loose. To remove the barrel nut you may be able to use the same strap wrench or maybe a yankee hill barrel nut wrench. Depends if the posts line up with the holes on the nut
I realize I'm late to the party, but I would also recommend avoid using a Map gas torch.
Propane maybe, but Map gas can be used for welding/cutting ferrous metals. I would think it would be too hot for this application.