Help! Foolish me playing mechanically inclined again.

If you can get two propane torches on it you might be able to get some heat to it, otherwise you need oxy-acetylene.

Penetrants need time to work, if they're going to. Don't spritz it with PB Blaster then slap a wrench on it and expect anything good to happen. If something good does happen, the nut wasn't stuck to begin with.

When time is of the essence, it's time to get medieval: Heat it, cut it off, or split it.