Waxer,
I have the same board as you, I've used a standard mast base (see pic below), simply unscrew the nut off it & the base will screw into your board. The sail I had up was a 5.6m, cruised nicely, hope to get in some small (<2")waves this weekend with that setup.
P.S. Prob would receive more responses if posted in the sup forum.
[edit] If you're going to get a rig, make sure the mast base & extension are compatible, there are a couple of different types. Best to get hold of a complete rig - see SB buy'n'sell.