I wanted to go 1.25 which really isn't avaliable. Speedway has from .25 to 4". I thought of stacking a 1 and .25 and I wouldn't have to get longer u bolts. I measured again and will probably get a 1.5 billet kit from somewhere that includes the U bolts. Mancini?
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?
I would only use blocks as the last resort. Always best to lower with the correct springs, or with adjustable height spring perch. Adding blocks to lower, will also increase leverage on the springs which will induce spring coil.
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.