Pontiac used cast rods in some of their motors. If this is your case, the most important thing you can do is switch to forged rods. You can build a very reasonable motor around stock parts. Use the stock crank, block, heads, and intake manifold. Use pistons to get the compression ratio between 9:1 and 9.5:1. Comp's XE262 or XE268 should make decent hp with excellent streetability with your displacement and a stock intake manifold. With the slightly larger displacement of the 400, both cams should also work with a stock torque converter . If you can find the height of the manifold, any manifold of the same height will work. Get some headers and a good carb and you'll be set. All of this in a properly blueprinted motor should get you to 375+ hp at the crank and 430+ ft lbs of torque.