Good to know on the u-bolts. I have been searching around and asking if anyone knew of a local shop that could custom make some u-bolts for me, but I haven't had any luck as of yet. I think I should be able to get bolts and plates online somewhere if need be.
As for the blocks, the 3/8 tapped hole will get a bolt threaded into it to replicate the head of the centering bolt on the springs. It doesn't actually bolt anything together, just keeps the block located where it should be. The actual head of the centering bolt will then rest in the 11/16 hole drilled on the top side. This should keep everything lined up as it was before. Welding the block to the trailer would just be added strength, since lifting the trailer will add more torque to that joint.