Hi Mike,
Are you using the Hatori flex header #796???.
I have mine in the fuselage.Where the header meets the pipe.I don`t think the vibration will increase,i use a hush clamp from Dave Brown the 60 size,there are 2 sizes a 40 and a 60.
The hush clamp has rubber isolation thus reducing the vibration,if you hard mount the header you could break the haeder because you are using a soft mount on your engine.And i think you could get a little more vibration too not so much!!!! because of the hard mount.
I have my header brace placed right underneath the END of the header,actually in the fuselage,you have to cut a hole in the fiber glass pipe tunnel so that you could screw the hush clamp in.
I have a lite ply brace and a blind nut so that i can screw the hush clamp in.
Greg.
www.arubarcclub.com