Don't need a headgasket. Dont need different pistons. Setup is good for 360-400 on stock compression.
Piggy back does 500bhp just fine. Your need a lower compression with anything over 400 though.
This kit has all the main mechanical components. Your need gaskets etc etc. Recommend for an oil cooler but not 100% required.
All your need is an ECU Piggy back to map it, and a decent clutch.
You don't want to get a thicker head gasket AND pistons, thats pointless. People run GTE lumps with 9.#:1 compression, lowering a GE to less than 9.anything:1 is wasted. To be honest, the US NA-T's run 600bhp with just a HG all day long. It has more chance of knock but they do use meth/water injection alot more from what I've seen on supra forums.
This kit + cheap piggy back / or refurbished AEM unit + upgraded clutch + new oil lines = job done, 365bhp minimum.
XS oil lines usually need replacing for slightly better ones.