Given the further discussion I think your best option at this point is to make or find used something like the blocks with curved tops as shown on the GMC in one of my earlier post. Given that you'll have a lot of more or less square U-bolts already on hand making something to fit is probably cheapest.
I made these for my front axle to mount air helper springs.
Think I started with 1/4" plate and milled the appropriate radius grooves in them at the proper spacing. Then filed the edges for clearance on the bend radius of the u-bolts.
You may want to start with 3/8 or even as much as 5/8" plate. I kept them thin because I needed the clearance.
https://picasaweb.google.com/lh/photo/XhpxTSOlop6_8t-sRPk_rNMTjNZETYmyPJy0liipFm0?feat=directlink
