I'd suggest using a trailer set up for your boat (easy if you have one), and using it as your guide. Otherwise...
I'm no expert on this, but learned a lot (still not nearly enough) when this trailer was built for my E22 about 4 summers ago. I've heard that suspending a boat (by the lifting rings) long term is not a good idea. That's why the bottom support like the one you have is best in a wet boathouse. The guys who fitted the new trailer suspended the boat just to clear the fenders, pushed the bunks flat against the hull and welded the bunk supports in place. If you have a trailer, the horizontal distances should be spaced equidistant from the centerline. Exact distances apparently aren't imperative on my rig because the boat can shift a couple of inches either way due to the flatness of the aft hull. I'd like it to be a little tighter (so the water inlet won't contact the bunk), but tighter may be impractical if the widest beam is in the center and not fully aft (which is probably the case). However, my trailer guides are at the very rear. It'd look weird to have a couple of guide bunks over the fenders. I'd try to measure mine, but I don't feel comfortable with my dimensions not working for you, which might cause the hull to twist, bow, warp or some other bad option. Here are two pictures to give you an idea what I'm trying to say:
