Probably no useful street power from any of those mods, although you can get a nice sound. For permanent performance/power improvement you first need a tuner, perhaps search the forum for diablo. There has also been several recent threads discussing performance. Many V8 owners here think the diablo is worthwhile with a custom tune. The engine compartment is narrow. Folks talk about doing this or that and you never hear from them again. The engine flows pretty good in stock form. Performance... look at the SRT, no replacement for displacement.
There are custom houses that will fit headers, if you must. You'll find one that will put a blower on for you

. But the WK2 is a heavy vehicle, not that suitable for racing in the streets. In my opinion, it would be less money in the long run, and a better return on your investment, to trade in your V8 for a SRT. The new ones with launch control are even more impressive.