I'm with Pix on this, I recently put an Eduard PE cockpit in a 1/72 F-4 by putting the etched part over the kit instrument panel, and then found that it stopped the fuselage going together as it was meant to.
I've just tried a Cutting Edge resin cockpit for the first time, having only ever used resin for conversion parts in the past, and I'm converted. If there's a choice, I'm going for resin over PE every time in future