Good pdf- thanks! I suspected that 45 degrees was about the max. My sine bars are certainly not lab grade, and may not even qualify for commercial. One is a Fowler, the other I've not a clue. On the good side, I can measure most of the things that matter, and have yet (in 40 years) to need angles known better than a few arcminutes. Since getting a set of angle blocks, the sine bar hasn't seen much (any) use.
It would surprise me if the block of cold rolled moves enough to detect. The aspect ratio is block-like, nothing like the aspect a straightedge would have.
I had another thought on the reference square. If one wanted a bigger baseline, it would be easy to start with a piece of iron pipe, maybe 4" diameter or so. There would be plenty of metal to grind a 1" wide flat down two sides and follow the same procedure as for the block type. Being a pipe, it wouldn't be crazy heavy like a solid cylindrical square. Hey, I'm all about cheap sources of material!