450 HP at the flywheel or at the rear wheels?
The LT1 mains are 2.45". The 400 mains are 2.65" Crank main journals need to match the block.
As noted above, 10.5:1 seems a bit high for a blower motor. I've seen some well built, high boost LT1's running in the 9.0 - 9.5:1 range.

 

Better keep searching your combo. Not much of what you said makes sense. Streetable 425 hp....10.5 :1 compression....STS Turbo..... your all over the place.
Like Dwayne said, look at the heads. You'll find power.
A very good place to start would be the book by hp books:

http://www.amazon.com/Rebuild-Small-.../dp/1557883939

It will give you an overall understanding of the LT1.

Then I'd start by looking at the head/cam package you go after. Once you've settled on those parts the rest (bottom end ) are easy to pick. You can cheap out a few hundred dollars with Lloyds stuff or for a few hundred more get an excellent package from AI. I have had both and I am extremely happy with my AI stuff. Top notch and believe me, there is a difference.

Good luck and happy building!

 

well the idea was to keep the boost down around 2-6 lbs unless i was pulling it out to race... i had no plans of running 14lbs all the time on top of that it would be a while b4 i can afford the sts kit and i want to be able to drive it after the motor was built w/o feeling starved for power. i can see the logic behing running 8.5:1 or even 9:1 for a motor dependent on the boost for power. but thats not my intentions. i would like the turbo to be only a power adder... if and when i get around to buying the Remote tubo kit

yes your right i did mean 10.5:1 thank you

 

just buy a compstar rotating assembly