newbie with supercharger question

First off, although both the Eaton and the Kenne Bell are considered “Positive Displacement” superchargers, only the Kenne Bell is considered a true Twin Screw, where the Eaton has been dubbed a “Roots” style blower. Twin Screws compress the air directly within the case itself, where Roots blowers “paddle” the air from the inlet end to the outlet and compression takes place within the manifold. Both do what they do well and both make great power within their designed parameters, but are still very different.

If beyond 400rwhp is your goal, then you're better off with the Twin Screw (Kenne Bell, Whipple) over the Eaton. There are only two companies that build Eaton based kits for the 4.6L SOHC and that's Allen and Ford Racing. The Allen uses an intercooled version of an S-ported M90 in all of their base kits and Ford Racing uses a non-intercooled M112 with integrated manifold. Bothe kits in base trim will easily put you into the 300-350rwhp range with a PI based 4.6L engine and the Allen will run head to head with the smaller twin screws right up to about 400rwhp with their 9psi GEN V kit. Beyond that, you've pretty much seen the limits of the smaller Eaton blower and you're going to either need to go with some sort of custom set up, or look into one of the Twin Screw compressors noted above.

That being said, forged parts are always a good idea. Your heads are already aluminum, so replacing them isn’t necessary. Having them ported by one of the more reputable companies (VT, Fox Lake, Patriot Performance, etc) would be your best bet. The fuel system upgrades are also a necessity at that power level, but there’s no need to replace your stock alternator. Although now would be a nice time for ignition system upgrades.

Have fun spending money.