My New 98 gsx build

[CornFed2.4]

What I'd do for 500hp

Stock 6 bolt or 98-99 7 bolt arp hardware on connecting rods
Gasket matched head with Evo beehives with GSC1 cams
L19s with permatorque
Billet 5858 cea
SS o2 housing w/gate provision
FP race mani
1100 FIC hi-z
255 rewired w/ BAP
Evo3 intake
N/T throttle body

I didn't add link, vrsf fmic, ect. Assuming you have that stuff

I think that would get to to 500 at DB.

As far as the manifold, go with the JMF street or Race if you plan on a 6266.