On the PB-Blaster, I'm not sure it actually helps but it can't hurt. My bolts were dry in the section where they threaded together when I finally got them out and I PB-Blasted them religiously every day for two weeks. If you're going to, make sure you get the PB-Blaster *above* the bolt hole - as in spray it angled up over the bolt and let it trickle down in, it'll get more in there than spraying from below and hoping for capillary action will. I think it at least broke the bushing liners free from the bolts as I started hearing a lot more creaking and grinding after a few days, but I know for a fact it did nothing for getting the bolt out of the weldnut.
As for bolt out of the weldnut - MoparManiac told me that he's had amazing luck using a flame wrench to heat the nut up cherry red and then using a breaker bar. He's only broken one rear shock bolt (EVERYONE breaks these!) and it was the one he was too lazy to use a torch on, and no leaf bolts. Just poke a 5/16" or so hole in the frame rail under the weldnut and hit it with an oxy-mapp torch (60 bucks at Home Depot) till it's a nice red color, then put your foot on the breaker bar and crank on it till it breaks free... keep it moving, don't let it sit for too long, and don't set your Heep on fire.
EDIT: and probably replace the bolts after torching them, it ruins the heat treating. You want grade 10.9 from an auto parts store, or if you don't feel like hunting them down, these are what I used (OEM part numbers):
4x part number 3420 2118 (bolt)
4x part number 1150 2814 (nut, get 4 in case you need to replace the weldnuts)
Google for people selling them, I got mine from
http://stores.zmjeeps.com but there are a lot of other sellers.