Hi I'm mounting a 65 LA on my GP J-3 and yes, had to grind a relief in the mount for the Slimline to clear. Also I am glassing the bottom center section of the wing, I too feel more comfortable this way. Later in the spring or summer I'll be getting a 4 cycle for it, maybe a Magnum or Thunder Tiger...what size engine (4 cyc) would be good? Thanks Bill