Most tool distributors sell a nut splitter that makes the job a lot easier. It's a device that fits around the nut, and drives a wedge into the side of the nut with a jack screw. I've used one for a lot of years on shock absorber nuts and exhaust pipe clamps. Running a die down over the U bolt threads should allow you to re-use the bolts, particularly if you don't intend to put the vehicle back on the road.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!