I love the 289 and I agree with the above post. Squeezing 450hp, even flywheel horsepower, is going to be fairly hard from a 289. The real great thing about the 289 is they rev for days when built correctly, and they are very, very stout motors as far as durability.
If you are serious, not just b.s.-ing but serious about getting 400+ horses from a 289, I would recommend the following route.
Get a set of good reconditioned K-code rods with 3/8" ARP wave loc rod bolts or a set of good aftermarket rods with the larger bolts. You do not wan't to be using the stock 5/16" rod bolts and thinner shouldered rods that the standard C and A code 289s came with if you will be revving the piss out of it.
Probe forged pistons, essentially the same ones you'd use for a 302/5.0L would be a great match. Part of my recommendation for this build would be a supercharger so using a deep dish piston with lower compression will be something to think about.
I'd use a set of AFR 165/185s with a custom cam, for a frequent driver you can go with the hydraulic roller conversion but if you want to primarily race it consider an agressive mechanical roller that will get those revs going. Contact Jay Allen at Camshaft Innovations or FTI/Flow Tech Induction and you can get a custom cam ground by experts in small block fords.
I'd recommend a Edelbrock Victor Jr. intake with a Holley 4150 style blow-through carb and a Paxton supercharger. Paxton makes superchargers for the 289 that will fit in an early mustang, fairlane, etc.
Make sure you have a good set of full length headers, a good ignition setup from MSD/Crane/Mallory etc. and a numerically high rear end gear like 3.89 or above, and you will make that power and scream in the quarter.
The sound of an 8000rpm+ 289 revving down the track sends chills through my spine.