Hitman, I would think a good 35 would fly an Avistar fine but to my notion it is not a trainer like a big slow flatbottom wing plane would be. I've had a couple and a strong forty will really make it move. My favorite was one with an OSFX46. Fine all around plane.
The OSFSR engines I've had were top of the line with plenty of power for their size. A 35 FSR shouldn't have any problem flying a plane meant for a bushing 40 like the LA series.
Fred