I recently posted some pictures of my masthead, with an explanation of how the emergency halyard works. See here.
Not sure what sheave they used for the F35, but the masthead on the F36 takes a Harken 500, which is the same as what’s in the mainsheet blocks. However, when I bought my boat I replaced it with a Harken 754 “High-Load Sheave”. It’s stronger, and a bit more sealed, so hopefully it won’t need replacement for quite a while.