I had Hagerstown Spring and Axle ,a shop that works on truck axles, make new longer U-bolts for me. They did it while I watched. The price was very inexpensive.
The only problem was that the didn't have any threaded rod in the original diameter (was it 5/16? I forget) so the new ones are 1/16th oversize and I had to drill the plates to fit them.
I told everyone that I got the up-rated U-bolts from Racetorations for many, many pounds.
No one believed me.