Hasselblad made several versions of sports finders, one mounts in place of the hood or prisim, and has a small mirror and an eyepiece that shows the center of the screen so you can focus.
I bought that one specifically so that I didn't need to rely on my guessimates in using it.

There are (were) masks available for various focal lengths on some of the finders, I'm pretty sure there was one at least for the 60.