Using a Torch

I'm about to attempt removal of the Y-pipe on a '97 Taurus GL wagon (3.0 2V "U" engine Vulcan) to replace the oil pan gasket. Along with that I'll be replacing the front cover gasket and probably the valve cover, intake, and maybe even the head gaskets (all Felpro). I bought this car new in '98 and it's got 205.7k miles on it now. The exhaust nuts/studs have never been disturbed. In preparation for removal, I've been heating up the car to temperature, letting it cool, then spraying the nuts alternately with PB Blaster and Liquid Wrench. Four days of this now with two days left before the weekend. However, I may need to resort to using a torch and I'm just wondering what precautions I would need to take to safely do that. I've never used a torch before on anything and using one for the first time in the engine compartment of an automobile seems kind of crazy to me, but nonetheless - people do this safely so I'm hoping someone here can enlighten me as to how to do that. I'm not even sure exactly how I might be able to even GET a torch on the firewall-side flange nuts. They're well recessed from underneath and only one stud head is visible from the top. Maybe torch one nut from underneath and torch the other stud head from the top???

So what is the proper technique for using a torch safely (and effectively) on a car to remove fasteners???