it's not that vtec adds power, it helps spread it out over a broader rpm range. vtec motors also seem to have better aftermarket support.
to use a z6 head, you could probably get away with your stock intake manifold and an odb0 vtec ecu. I don't know exactly what you'd need, but there are sites out there that show how to build it. Just try searching for "mini-me swap" or something to that effect. you're going to find a lot of info about putting a z6 or y8 head on a d15, but the process is basically the same.