2:1 Halyard block

[SVNeko]

I am about to replace my main halyard (at 2:1 on a tall mast, its a $$$ piece of lo-stretch rope) and will also replace the halyard block, potentially with one of the new all in one shackle/blocks. Since the existing block is an old Fredericksen one for which I have no data, I am at a loss as to how to assess working load needs. Any ideas? Or do you think any good block will be more than strong enough for this application?

[Sailmonkey]

I've always been curious about the wichard MX halyard shackle. For 2:1 it without a sheave!!

[SVNeko]

Every image I've seen of that one has a dyneema line in it, which suggests its best for slippery stuff. I think I prefer one with a real sheave, like Tylaska or Antal. I use solid blocks for my spin sheets, and they don't run as smoothly as I'd like.

[CAELESTIS]

I use the Antal with a 2:1 on a 50' boat. Works great.