The rig I will be using is from my 16ft skiff (Aussie high performance skiff). The rigs, #1 & #2 (both rigs are usable-- I intend on 'stumping' my #2 rig) have approx 5ft of fibreglass for the tip and carry big asso kites. They also have double spreaders and lower stays--well supported for what we intend to carry on the i550.
Yes this is my boat--sold it only a couple of years ago, but I kept a lot of the gear from it. Check out the Australian 16ft Skiff website. A quick tip---the prices for gear seem pretty high, give them a call anyway if you're keen and have cash in your pocket ;) deals tend to work out better at the end of the season. Keep in mind, that fibreglass mast tip retails for almost $600, and you could pick up a complete rig and sails for $1500 ?
The main sail for a 16ft skiff is no good as there is way too much pre-bend used in the rig on the skiff. Stand it up straighter for the i550 and you have a good strong mast. You should also be able to use the jib intended for a 16ft without too much drama.
The 16ft skiff 'long' centreboard will be used as a rudder for "Shazza" with no need for any modifications at all!!