New engine or rebuild???

If you want 450+ HP on a 5.0L and wondering about a rebuild, I would suggest a 331/347 ci. Long block with forged internals from Sportsman or Dart... That way you would have a foundation that would hold a **** load of power!

Yep i'm with the previous guy. By a good block cause u'll need it. 450 hp sounds like it going to be blown so if it where me i would do a (see sig i'm bias) Dss long block 331 with ur choice of heads (tfs tw, afr etc) and a procharger w/ intercooler. the intake is up to u, b/c theres alot out there that will get the job done. That's what i would do. I like the 331 opposed to anything else.

450+ hp with engine accessories isn't a far stretch, but building an engine with that level of power naturally aspirated is going to make for a few driveability issues as well as reliability concerns. You have to run some pretty good cam timing to make those figures.

If your car was a fox body 87-93 I'd say build/buy a 331 because they don't weigh as much as the 94-95. With the '94 I suggest a 347 for the extra torque they provide.

If the car was mine and all I wanted was 450fwhp here's what I'd build:
331/9.0:1, Comp XE266HR, AFR185, RPMII, 36#, supporting components and a 6psi charger .... plus an EECIV out of a fox body .... there I'd be at 450+hp.