If you want an honest 400HP at the tires I'm not seeing it using stock iron heads with stock valve sizes etc.
If you want to use stock heads without spending $2k on porting and preparing them you might as well do a quick valve job on them and put nitrous on top that's the only way I see 400HP at the tires.
If you want to make 400HP on the motor the cheapest way there will involve a set of Edelbrock heads a good hydraulic cam and a stockish shortblock with 9.5 or 10.5-1 compression measured.
Your torker intake is wrong for a 2000 convertor, 3.55 gears and 4000lbs. your 800 DP is also wrong for those components.
I would not use the Six Pack replacement pistons as suggested many times above. You can use them but for $100 more invest in a lighter set of pistons and your engine will live longer.
If it was me I'd build a stock shortblock except for something like Diamond flattops. I'd sell the Torker, 800 and all those other BB cast iron. Then I'd get a set of Edelbrock heads and a used Holley Street Dominator intake or an Edelbrock dual plane. When I had all of that stuff figured out I'd come on here for a camshaft and carb. recommendation. (and when I think about it, I'm not so sure there is a camshaft that will make 400HP at the rear wheels and will work with a stock stroke 440 and a 2000RPM convertor).
And like I say the other way is to ball hone it, get a valve job done, stick in new bearings, use the Torker, and put a nitrous plate under the 800.

Sheldon