I know exactly the block you are talking about. Mine had one there too - it was riveted inside an eyestrap. I never did figure out what in the world that was for.
Here is a poor quality picture of it back when I was using a single line for the mainsheet and traveller. For those of you who don't know or can't make it out in the photo, there is a single block hanging on the eyestrap off the back center of the rear beam. Any ideas what this could be used for?
-Rob V.
