I don't know if you've figured anything out with this yet, but I just got done dealing with a similar issue. my trailer came with 2" blocks, and I've been running them for the 2-3 years I've owned it without any issues. 9/16" u bolts though. The blocks look to be home made, they're just chunks of solid 2"x2" aluminum drilled and held in place by longer spring locator bolts. I still needed a couple more inches so last weekend I swapped out the stock 4 leaf 3500lb springs for the 6 leaf 7k lb springs. It gave me just shy of 2" more. So just about what I was looking for. I took it on a quick drive and with the heavy springs it still seems to ride smooth. I occasionally pull doubles so I was planning on upgrading suspension and eventually axles anyway. I have a few pics, but not sure the easiest route to get them uploaded on here.