Hy Tango, I have seen many "spreader plates" on the top of spring packs, some to adapt round "U" bolts to the flat spring surface, some just flat plates with notches on the edges for the "U" bolts to sit in. I suggest you make up some flat plates that contact as much of the flat section of the "U" bolt as possible and install them between the spring pack and "U" bolt. The only alternative I can think of would be to take one of your old "U" bolts to a shop which supplies/fabricates "U" bolts and see if they are willing/able to do the forging to duplicate them, hope that helps.
As a Toolmaker I would agree with this approach.The added plates would fill the gap and spread the load across the top of the spring.
I would be hesitant to heat those U-bolts as you do not know the steel type or heat treat they were subjected to.Heating and reforging them flat could affect the strength.
Why take that chance?
