just won this kit last night at my club meeting so I checked the plans the kit version has webing on both sides of its motor mount. when I have mounted my motors the webbing has been on the bottom it seems to work fine . I also have a NEXTAR and have used the iso smooth mount on several of my OS .46 planes ( I have 3 ) purchased extras from tower hobbies for 4 bucks . like Ken said 1/4" should be enough clearance check your pic. on the box . the kit version has great instructions and plans, might want to check with SIG they might be of some help I am going to throw mine together in the next few weeks