My spinnaker halyard runs to the bottom of the mast, but the block that allows it to exit the mast is partially blocked by the jib and boom vang tensioner (whatever that ancient winch-like system is called). Meaning, the line cannot cleat to a fitting on the centerboard trunk, where nearly all cleats are, without passing through another block first.
What kind of system was originally used on these kinds of boats?
Is there a modern system that’s simpler?
Oh, I had forgotten that you have the
rollers for the jib halyard and the vang (that's what I've called them and everyone has understood what I meant). I had them on my 1980 Fountaine Pajot; changed the vang almost right away to a block system, and did the same to the jib halyard a year later (although I have to admit that the memories are quite hazy by now

) I think it was a "French" thing, and the majority never used it for the vang, Many more used it for the jib halyard, but even that was
passé by the late 1980s.
We could have a long talk about the mechanics of the roller system itself, but that wouldn't solve the problem at hand. One quick fix would be an additional single block for the spinnaker halyard above the exit block to lead the line over the roller attachment; another would be to simply cut a notch to the stainless attachment plate. Even then the halyard line may still chafe against the vertically-running part of the vang wire, so a long-term solution would take the halyard somewhere else, out of the way. What's the cheek block on the mast for? Is there another one on the other side?
(By the way, I think that the vang block on the mast was intended to be attached to that horizontal eyestrap.)
Also, currently I’m using a jurry-rigged 2:1 downhaul that I would like to replace properly. Have any insight there?
With "downhaul", do you mean main cunningham? It's not that important of an adjustment (you actually tension it in overpowered conditions only), but a 4:1 is still nice (and standard). Typically you'd have a 2:1 at the cunningham eye (deadended at the gooseneck), another 2:1 along the centreboard case, and a cleat on top of the case.
Went sailing for the first time (on the 470) this season! The boom is a lot higher than I remembered it being, even with the mast raked all the way back with the chocks. Or maybe I’m just used to the low boom on the Hobie. I’m starting to look at these finer adjustments (maybe boom height isn’t a fine adjustment

).
Well... boom height is largely dictated by mast rake, which is a major tuning variable. Done any rake/tension/bend measurements yet?
_