What I did to one of my Infusion crossbars that I kept, figuring somebody else would like adjustable down the road and my standard one was setup correctly, is take one of the Nacra 5508's mentioned above and shown in this photo here
and pin that to the crossbar then insert the urethane tiller on the other side. It took a bit of fidgeting to get the diameters sorted and its heavy but it does work well.
The right thing to do is probably install one of the Hobie 20 threaded crossbar endcaps into the aluminum crossbar (would need to double check the size) then machine a fitting with the correct threads for that endcap on one side and a hole for the urethane piece with its plastic housing on the other (this is where the pin goes through to remove the setup from the boat). Optionally, and probably smarter, is to effectively bond or screw a threaded stud into one end of the tiller crossbar and machine that same fitting but with a threaded hole for the stud. I say that as I could machine that fitting in a few hours on a lathe and use a 316 stainless fastener in the end of the tiller, where as machining external threads is painful. See the Hobie 20 kit here: https://www.murrays.com/product/07-1953/
The alternative is to run the complete Hobie 20 style setup, which is similar to the Exploder setup. You would have to cut down the Nacra tillers and install pins, which isn't a trivial job but do-able. The big issue I see is the length of the tillers, there is a sort of minimum there in terms of force required to turn the rudders. On some of the boats you could order Nacra 20 tillers but its gets tricky as the ackerman angle is built into the tiller bars on a modern Nacra.
And I have no clue how much that matters but I will say that if you can lower drag in a turn on a race boat it absolutely does matter. Keep in mind on an F18 in breeze tacking upwind you are looking at boat speeds from the top teams in the 12.5-13.5 kt range for an upwind VMG of 9.5 kts assuming a tacking angle of 90 degrees (we run tighter than that but only in flat water). In a tack you are probably down to half that in terms of VMG, and a very good tack is still a 20 second operation before you are coming back up to speed; we can take a minute to accelerate back to max speed. Lets call it 45 seconds at an average vmg of 4.5 kts during the tack. That translates into 360 feet or 20 boat lengths lost in what I would call an average tack. A top team can probably get it down to 5 or 6 boat lengths, but if you have additional drag from the rudder system that could impact that further with less ability to turn the boat easily. Add in some waves and any additional drag from +20 deg to -20deg head to wind could have you stopped dead which would spell disaster.
This math also shows why tacking on high performance boats must be done smoothly and quickly, and why it should also be avoided whenever possible! The problem gets worse at higher speeds, if you watched Glenn Ashby at the last A-Cat Worlds fully airborne upwind he would go right for the layline and one tack it to the market at a boat speed in excess of 21 kts.
All of this probably doesn't mean much to the OP's original issue or long term plans, or most folks sailing recreation ally though having a proper rudder system setup tends to be more enjoyable with less force on the tiller during long outings!
