These guys?
https://www.speedwaymotors.com/Speedway-Aluminum-Extruded-Leaf-Spring-Lowering-Block,3353.html
If you wanted 1.25" I'd get a 1/2" and a 3/4", since the 1/4" ones don't appear to have a pin. Those two would be held together by the center pins. I'd still probably put a couple of tack welds on them once I had them installed and confirmed it was the height I wanted, but I can weld aluminum so it's not really a big deal for me.
So you already have 1.25" of threads hanging out the bottom of the nuts on your U-bolts?
With 1.25" of block it's not really going to be much of an effect.
Lifted trucks run blocks that are 4" - 6" tall all the time, very common. Heck the old F-250's were called "hi-boys" because they came straight from the factory with 4" lift blocks in the back.
Why? 1.5" blocks are readily available, just see the speedway link.