I believe the lengths are different. Murrays sells two different kits, one for the std 18 and one for the SX. I don't know if the difference is because the hook to mast at a different place because it's taller or if they're shorter or both. I added wings to my boat and I have adjustable hooks but even when they're adjusted to the top it seams to be low. I would love to know how much shorter they should be but I don't think I would want to shorten mine for time I take the wings off.
'79 Hobie 18