If it's of any interest, I had to work this out too. I have the drum mounted just above the level of the deck under the housing shown:
There is a continuous loop of sheet which comes out of the house and around the deck running on blocks and then back in at the other side.
There are loops in this sheet to which the sail sheets are attached - the main sheet attachment is out of shot to the left here but you can see the jib sheet attachment (unused) at the far side. The sheet's then run through blocks again to a final eye from whence they go to the booms. Note that when these pictures were taken I was still only trying stuff out...the granny knots are done properly now
I've just taken another picture of the whole thing......
The idea of the continuous loop is that it's always under tension and so can't come off the drum or snag.....famous last words.
I hope that helps give you some ideas....I'm sure people will speak up if I've done anything horribly wrong