We have a similar system on the new (to us) J/112e, I'll get a pic this weekend. Basically one flying lead for the inhauler, and one for the leech up/down so you can position the clew in 3D. We're working on figuring the boat out but so far it seems very intuitive.
That's my post on the J/109 forum. One thing you may want to try before drilling holes is rather than the aft end cheek block & cam cleat screwed in the cabin top, use a block that has cam and becket tied around the rope clutches as a temporary anchor point. You can then see how the rest of the system works. I've seen some use a padeye to attach this setup at the aft end so there is no need to drill separate holes for the cheek block and cam cleats.
Here's a pic of our system at the jib clew, the inhaulers are very similar to WHK's setup except it doesn't adjust both sides simultaneously. 4:1 on each side of the cabin top to a 3:1 after the turning block. The up/down control is cascaded 4:1 -> 2:1 -> 2:1. With so much mechanical advantage it is really easy to adjust.