Hey guys, if you're looking for floats for the T-cart check this site out. Lots of size options and your choice on how to finish them.
I would go with the flat bottom floats. They might not be quite as scale looking as the V bottoms but water handling will be much easier. Just apply a little power and they'll pop up on the step and you're off. I would base the size on 75 to 80 percent of the fuselage length from the back of the prop to the rudder hinge line. Maybe John R. can provide us with that measurement. Overall length is 36" (probably from the tip of the spinner to the back of the rudder) so prop to rudder is approx. 33". 80% of 33" is about 26.5", so 26" to 28" is right. Also make sure to have approx. 3" to 4" of float extending forward of the prop and, for flat bottoms, just a touch of toe in. This formula, originally published in RCM by Chuck Cunningham, has proven to be very successful and the guide I have used for more than 20 years of float flying. I'm charging my batteries as we speak and will be heading out to do a little float flying this afternoon.