Walter, is the venturi setup the same as on the 56, does it look like the UHP will fit?
I am a believer in the low RPM High pitch approach to 4 strokes. I think my 56 is right on the edge with a 6 pitch prop and will shortly be looking into something at 6 1/2 or 7. I am also going to somehow incorporate an adjustable venturi like I did the 40a.
I have both a Tom Dixon venturi and a UHP, neither one lends itself to being easily modified to be adjustable. The Dixon looks like an upside down bell with pretty thin wall thickness and the UHP insert has to have a thin wall to fit the manifold. Not enough meat in either one to thread for a nylon screw. Will probably use the UHP and make an insert with a flat side so it will clear the manifold.
With an adjustable venturi and the right prop you can tweak the thing to the lap speed/RPM you know works with your setup in any conditions.