That engine looks like an old Kawasaki to me.
Yeah mrB, you are right, it is a Kawasaki 350 Rotary Valve Twin. I think it was setup like the Avenger (or was it the Samuri?) Anyway, the American Eagle used the Kawasaki 350, 175 and, I think, some others. As said, the also used the Laverda. I always kinda wanted one of those Kawasaki 350s, they were pretty good screamers. Never managed to get one though.