Axle and trailer mfg don't come with suspension blocks nor are they a option on std leaf spring suspension
I've lost my email answer from American Rockwell axles. They and Dexter have said they don't recommend their use on their axles.
Even big rig trailer shops in this area wouldn't add blocks over 1" on these type of trailers. Anything over 1" they over sized the U bolts with special alloy made for this application/thicker top plate thickness and heavier spring keepers..... and they wanted me to sign a liability disclaimer.
I refused.
On this particular trailer I needed 2" so they cut the spring hangers off and added 3/8" x 4" wide x 12" long steel plate with two sets of holes. The frame is a stacked tube type and works well with welding the longer spring hangers.
The safest way is a sub frame made from steel tubing welded to the trailers main frame rails if over a couple of inches.