The manifold is almost a duplicate in design to the old n/a 13B, what I mean is no separation from rotor to rotor. The manifold is a straight dump into a collector.

I have seen 80 hp gains from a custom made header. All was done was adding 3 " of straight piping from the port. " No collection till farther down".

So with some good mods, and being they are rich stock, you should have no problem making 300 HP @ the crank.