I bought this hardware - the rings are sized at 1 inch (I think - although at the time I bought one at one size larger - they just have to not slip through the cringles in the mainsail) - the blocks are sized to the existing reefline installed on the boat.
I re-routed the existing single line reef so that the line ran through the new blocks instead of completely through the sail.
Here's the clew end as it would look when reefed:
and the tack corner when reefed:
Here's a view of the tack in the normal (un-reefed) position:
And here's the clew un-reefed:
The toughest part was fishing the reef line through the boom to get everything on the desired side of the boom (with the dutchman, the sail wants to settle in a particular manner, and I needed to place the reefing blocks on the starboard side to have everything sit nice). There was a messenger line present in my boom (courtesy of the folks that rigged it initially) and pulling the reef line through worked very nice.
All in all a very easy, $20 project that has made reefing a real smooth and easy thing to do.
Good Luck!