Well i purchased this airframe only, at a local hobby store(just had to have it) and i have both a 75ax and a 120 ax ,the holes are predrilled in the firewall for the mount, but the mount with the plane is too narrow for the 120 to fit, when any of the holes are aligned. So i tried the 75 and it fits perfect. This is my first time mounting a engine inverted so i want to do everything right! I was kinda disappointed in the mount (size) it seems a little small for that size engine ,and i have seen others make that comment on here! I really want to use the 120 but i just want it to fit correctly!