One other thought, Craig..
You show your spinn pole downhaul attached fairly close to the mast..
The advantage of this arrangement is that you will require fewer adjustments of the downhaul as you trim the pole fore and aft.
The disadvantage is that there will be little to no forward component in the downhaul pull. A downhaul mounted forward on the deck (ours is near the
jib tack fitting) makes it more of a "foreguy" and the advantage is that when you snug the downhaul tight it tends to pull the pole up to the
spinnaker clew/tack. This makes for a more stable sail, and one more job your bowman won't have to to (i.e. push the pole along the guy to the clew)
The disadvantage then is that virtually every pole adjustment fore and aft requires a followup or simultaneous adjustment of the downhaul. Once the crew is used to this it's not too bad, and IMO the forward pull advantage outweighs the cons.
Just something to consider before you start drilling holes in your foredeck.