No 1 Mk III scope mount
I played with a B-Square scope mount for the No 1 Mk III a few years back, and it was not a great mount. It didn't fit well from action to action, and it was difficult/impossible to get it mounted level to the action. On the other hand, I have had great luck with their mount for the No 4s and No 5s. The two mounts are not the same. As far as price, before you decide whether it is too much or not, find out if it comes with rings. I know many of the B-Square mounts came with a decent set of scope rings that should be worth around $25 - $35.