The 40LA isn't as wide as the 46FX, so I think you'd end up having to drill new holes in the firewall, but I think the holes on the mounts themselves are the same distance apart (front to back) so you'd be able to use the same mounts... you might want to go to the OS web site (osengines.com)... you can download a couple of pages with all the dimensions for the various motors. I've got a 46FX on my 4*... lotsa power!