Yeah, as others have said your best option for a N/A combo is 38 CC TFS heads with cams (13:1 comp), headers, etc... that would net 320+ RWHP, but honestly for the kind of money and time required to make that kind of power why not piece together a
Vortech kit?
You could likely piece together a vortech kit for $3500 including everything and make 380+ RWHP.
A guy my car club has a 96 Mustang with a WAP alum block, TFS heads, Bullitt intake manifold, and MHS stage 2 blower cams. He set it up for boost (9:1 comp) and laid down only 262 RWHP through the stock cast iron manifolds. I was able to get 240 RWHP by installing MHS stage 2 NPI N/A cams. The point I'm trying to make here is that based on what I've read on these forums, I believe people have been overstating/exaggerating 2V dyno numbers for years. Depending on the dyno type, it will also play into your numbers. I'd likely make over 265 RWHP on a Dynojet with my car, yet it only made 237 RWHP on a dyno dynamics unit.
I'm really more curious about what your goals are for the car you have. If you want a fun DD, then PI heads and cams will do that no problem, if you want to tear up the track then I'd suggest a vortech kit. The last thing I want to say is that a dyno is nothing more than a tuning tool, what you do at the track is what really matters.