First, welcome to CHR, good having you here. Seeing as how you're looking for torque, I'd suggest (as the others have)taking a look at big block... The numbers you're after would be quite easy with a big block Chevy or the big 500" Caddy engine..

However if you're set on a small block, then with all the boost that twin turbo's make you would be much better starting out with a Dart block for the added strength. Turbocharging also requires a camshaft ground specifically for turbo's, and the compression ratio of the engine needs to be down around the 8:1 area. Turbocharging also requires a lot of carburetor mods, so you'll need one that is set up for "blowthrough" operation. Also on your shopping list you'll need an ignition system that puts out at least 40,000 volts to fire that highly compressed mixture and also an ignition box with it that has a retard feature for the timing...

I would also suggest before you part with any of your hard earned money that you start the project with a lot of studying on turbo systems and their requirements, lots of good books out there that cover the subject and aren't just written to sell you parts like the neat ads and pictures are intended to do...