as Ross stated, they need to be as long, if not a little bit longer than the factory mounts. you can actually use some tail blade spacers in between the canopy mounts and the frames to space them out a little (i do this on every one of my helis).
another thing i do....once i get my canopy mounted, i take some of that Styrofoam PVC pipe insulation for 1" pipe, and split it down the middle. so i have to pieces shaped like a "C". i install my canopy, and put one piece of foam between the main gear and the canopy on each side. then i take my heat gun, and warm the entire area up on both sides. i even warm up the front of the canopy and where the mounts go into the canopy. this will open up a little more space. just be careful not to get too hot an damage the canopy or the paint. the fiberglass can be formed to fit by doing this, and you will never have an issue like that again......
