Easiest way? There is no easy way
But, if you want to avoid having to air hammer/ chisel / drill, do the following:
1. Drop the gas tank. Be prepared to snap a couple of more bolts doing this (front carriage bolts will most likely spin and will require some sawzall action).
2. If you don't already have one, buy a $20 MAP torch.
3. Heat shock bolts till glowing with torch.
4. Remove bolts.
If you don't heat them, they'll probably just shear right off. The gas tank removal seems excessive to most, but trust me, in the long run, it will save you ton's of time and grief. Plus with the tank down, you can scrape some of that rust off of things and get it sealed up before the cross member & whatnot rust away.
DO NOT use the torch with the gas tank installed. Seriously.