I'm not sure if it will work, but if your prop is just a standard pin prop with a 12mm shaft you might be able to use a higher pitch prop. The standard prop for your boat I think is 7 1/4 dia 4.5" pitch which is great for pushing a 2000lb boat, but a 300 lb TI you can likely go to a higher pitch ( I have a 7" pitch on mine, but it came with a 4.5" pitch)
The one at this link is from Solas and it's a 6 inch pitch ( http://boatpropellers.iboats.com/Tohats ... (All_Years
There are only one or two plastic prop manufacturers out there so nearly everyone uses the same props ( Mercury, Tohatsu, Nissan, etc). I have an extra one in my garage if you want me to measure it up I can to find out the shaft dia, distance to from the back of the prop to the sheer pin, sheer pin dia, etc.
I only found 1 plastic prop for Honda 2.3 with a pic on ebay ( http://www.ebay.co.uk/itm/Honda-Plastic ... 3ccbdd9393
) and it doesn't necessarily look like yours in your pics. The prop in your pics looks to be a hub type, is it custom.
Here is a pic from the Honda marine website of the prop that comes with the 2.3 which looks like a standard pin prop.
If it would work you would definitely get a lot more speed, at the worst your out $14 bucks.
I know on my 2 hp motor going from a 4.5 inch pitch to a 7 inch pitch speeded me up 2 mph, however my 2hp putt putt motor now cannot get to the right RPM (not enough horsepower, I should have got the 6 inch pitch).
I'm just interested because I really want one of those Honda motors really bad, I will duplicate your motor mount, I love your design.