1080 would be o.k., but there are better tool steels out there, you can check your old broken piece for hardness.....try scratching it with a sharp knife.....that will tell you what you need to know right away..........
There are some tool steels harder than 1080....check with a local machine shop.......they can tell you what's available and its hardness.......
T and M Grade tool steels are used for cutting tools and are very good, F Grade Tool Steel is water hardened and is also good and not as hard as the T and M Grades.......some are oil hardened and some water or air hardened.........like I said on the earlier post, I don't think you want a piece too awful hard, as it needs to be a wear item and I think the yoke is the flexible link in the mechanism....the rotary bolt is not flexible, nor is the lever or stem, so that leaves the yoke....if it is too hard it will be brittle and crack again sooner than a softer steel......all metals 'age' harden with time and are succeptable to cracking, that is probably what happened to your original yoke.....IMO......
