I think it would be no problem to hit that horsepower level. Just off the top of my head, I'd figure on crossbolting the block and hard-blocking it up to the water pump holes. If you can find a thick block to start with, so much the better. The 4.25" stroke cast cranks are known good to 700 HP, so if you go with one of those and some good H beam rods, along with forged pistons from a reputable manufacturer, you should be good from the short block side. Since its a bracket race engine I'd be looking at around 13:1 static compression, with a cam in the 265-275 @ .050" range. You should get some heads that flow in the 320-330 range at .700" lift on the intake side, and I'd probably go with the 2 1/8" primary Hooker adjustable race headers. A good single plane like a Victor with a Dominator, or a tunnel wedge with two 660 center squirters, would probably be required.
650 HP out of a 445" engine is less than 1.5 HP per cubic inch, so I think it is definitely do-able. JMO - Jay