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Just a heads up on the float mount….. if they mount the same as the 801 (which I think they do), the front mount bar will likely affect your cowl exit airflow. If you are going to mount an air cooled engine, take this under consideration, as you might end up need to make other adjustments to compensate for this.
I have the IO-375 (low compression pistons, 195 HP), which produces a lot of heat. Knowing this at the start, I built with a larger firewall mounted oil cooler. I originally flew on wheels, without the float hardware. This configuration worked pretty well. When I installed the float mount, the cowl exit area was effectively reduced and I had trouble with hot temps. I ended up adding cowl adjustable flaps which allowed for increased exit area.
Pic shows the yellow mount bar across the cowl exit, and also cowl flaps.
Dave Beaulieu (on this forum) has a 750 STOL with a UL power engine on floats. I think he could probably tell you more precisely what to expect in your situation. He also did a very nice write up in the floats forum providing some performance information for that combo. It is a must read.