Unionville Turbo Beaver
I'm running a ST90. It's the older round head one. Plenty of power. We are at sea level. I tried using one of the long Higley needles but after it broke off the second time I just forgot about it. It has been flying for a half dozen years at the same needle setting both from the water and the snow. I run a 14 x 6. It's been a while since I weighed it but 17 pounds with the floats stands out in my mind. It is no problem at all at that weight, cruising at perhaps a little better than half throttle. I remember 37~39 ounces per square foot so a little math would show if those figures gibe. On that much wing the loading is no sweat. Seven servos are used.
I used a small bit of tail weight. I think I have a Sullivan soft mount in there so it would add a bit of weight.
The ST is side mounted with a pitts muffler. The head protrudes. I don't really notice the muffler so without looking I can't say that it sticks out much but I recall having to do some cutting to fit it. The 120YS should go in there OK, side or inverted.