Ill agree with most of the people here, just boost the b16. Ive seen videos of B16's pushin 600+whp and holdin up just fine.
You'll also need to consider traction though, theres no point in pushing 600+whp if you cant get it to the ground. Remember that. Just like that srt4 at the track, 500whp, and ran a 15.5. My h22 should run a 15.5 @ 6200ft (altitude). I think you can build a b16 block for $1500-$1800 (after machine work/labor), and the head for probably another $1500-$1800 in labor and parts (if you do larger intake/exhaust ports, machine the head, 3-5 angle valve job, valves, retainers, springs, cams, yadda yadda) Then piece together a nice turbo kit, and get it tuned to 12-14psi and youre set. Total build shouldnt be more then $5000, including axles, and a clutch/flywheel to handle it.
PRICES ARE ON THE HIGH SIDE, just sayin that you can build a b16 to be a hell of alot faster then a k20, even if you do ALL the most exspensive parts.