450hp from a 331 is doable, but you’re going to sacrifice some low speed torque and driveability in order to run a cam profile that will deliver at higher RPMs in my opinion. Also, the stock Ford blocks have a terrible reputation for cracking through the main webs when pushed over 400 HP for extended periods. You can easily build a 331 pump gas engine that will produce 410-415 hp / 425-430 TQ under 6,000 RPM and unless you are ringing its neck continually at the track, it should last you many years. I’ve never been a fan of stock block 347’s due to the reasons listed above.
The engine I built for my GT40 was a pump gas 331 with Webers that produced 415hp / 430tq - idled reasonably well with a mild lope and had a very flat torque curve. I liked it so much, I just built another one very close in specs for my 33 Ford Street Rod.
Edit - link to my build page with engine info follows::
http://www.gt-forty.com/GT-Forty/DRIVELINE/Pages/Engine.html