The P-heads are actually great heads...IMO. Vince just had a bad experience and mine have only been good. I used to run a set that were milled and had stainless valves installed. The exhaust side was opened up to allow a little larger valve. I put about 2+ years on them and countless miles. (The speed-o never really worked right!) I only pulled them, because the compression was going to be to high for the SC that I was putting on. With a stock bottom end, E-cam, the P-heads, and Cobra intake, I put 300 to the rear wheels. I replaced the P-heads with the GT-40s, Performer RPM intake, and Novi1000 (9ish #s) and put 400+ to the rear wheels. I don’t think you could ever see 400rwhp without a power adder. You might be able to, but I don’t think it would last very long or be street-able. If you want 400na, you should do your homework on the 351. If you just want 400rwhp, get the SC and be done with it.