The 4* mount is VERY strong. I did the same exact thing, TT 60, then a Saito 100. I just moved the Saito back, so it's front mount holes were halfway between the TT's. Unfortuantly, I pile drived her in a full speed from WAAAY up, must've been doing 80 or 90 went she went in. Plane was totalled, had to dig the engine out of an 8 inch hole. But the mount survived unscathed.