371 build W/Big Mouth heads
STIXX, I have heard of those places. Were you here in the states long?
On the BM heads, I figure that if you got them in the first place, your attempting to move some air, not just a little. And/or spin the engine pretty good.
As allways, smaller the engine, the more rpm you will have to turn to effectively use the head. There is enough cc's in the head (on paper) to support a good bit of engine.