Not just the head, you also need to modify the lower legs to add the two micro-missile ports and of course add the speakers on the shoulders.
Graham
The VF-19Kai already has micromissile launchers in the legs. And it has speakers in the shoulders, but they're not exposed.
The VF-19P fires it's micro-missiles out of two hexagonal openings (ports) located on the outside of each lower leg. The VF-19P does not have the same opening weapons bay doors in the lower leg that the VF-19kai, VF-19F/S, VF-19A and YF-19 have.
And yes, I know the VF-19Kai has speakers in the shoulders. However, the point I am making is the "Lawrence" Speaker system on the VF-19P is located on top of the shoulders nacelles on the VF-19P, it is not internal.
Graham
Don't forget also that there are fins on each leg, also, which are not on the Kai.