If all you see yourself doing is 300hp, I would stick with a Cometic Headgasket and ARP studs. You don't need more than that to hold 300hp on a 2RZ. Some people have done more with just that. If you want more, you can definitely do a built head and pistons, rods, etc. Check out Paradise Racing, they will have a massive list of things for any power goal with a 2RZ. They have built several to 1200hp or more. LCE is also a good one to check out.