Yes, deffo a big difference. My recent engine build, I just got the 4x4 cover and just bolted it to the 2WD plenum as its the same. Its bigger and flows better than the 2WD.

You're better off just getting a 4x4 fuel rail and moding the end to accept the 2WD regulator, or you could chop the mounting lug off the old 2WD cover, weld it to the 4x4 one and still use the 2WD fuel rail. But its more hassle.