Personally if I was building a special with an RD motor I would be looking at the TZR 3ma frame, its been done before and you wont have such a problem with the top two exhausts.
As to the gullarm...anyone know of someone who as ever fitted a CBR400 gullarm to a NC30 frame...I have one ready for the 500 but am also a little concerned about the offset rear shock, cant see it being a massive task though.