Sure it's all right to leave off the tips, may even increase the roll rate a bit. A Sullivan should work all right. If you haven't built the wing I would suggest that you change the turbulator spars from balsa to hardwood as they tend to break easy if you grab the wing wrong. Also go to hardwood on the turtle deck as that's a weak spot also. Here's some other mods that I would make and I came to these from the one I built. Increase the control surface by 25% for a more responsive plane. I had a TT .46 PRO on mine and it was a perfect match up and even built to the plans the plane is a real winner. Lost mine to battery (Rx) failure, broke my heart!!!! Have fun with yours.