Dang U-bolts!

run a wire brush/die grinder over them first,run a tap (backwards) over them w/ plenty of lube next
repeat till tap spins up by hand
then clean lube, andput never seize on the threads well first (before breaking anything loose)
break loose by hand, tighten, clean, repeat
you will never break a u bolt,
or just split at the top w/ 4" grinder and drop in 5 min
all depends in the u bolts, how much replacements are, and your pocket book depth