The heads are much more advanced in the LS motors, 1st of all they are symmetrical as opposed to our old BBM, the assembly is lighter, rods,crank,pistons, the intake and injection system that GM perfected is way ahead of any FI that the aftermarket has, heck get a very tuned carb and it will outperform the modern FI from aftermarket. Don't get me wrong for what they are the 400 BBM is a good motor, I put together a 451 that has street manners easy to drive and made 610hp & 625tq, amzing thing that the LS can't do as well is the torque @ lower RPM how about 543lbs @ 2800 and stayed until 5800 getting 540lbs over 600@3700up until 4700. The modern engines are a completely different animal, Your goal can be accomplished and I would say AndyF has proven it with very respectable builds over the years but at the price of driveability. Stroke it to either 451 or 470 and you will be more than happy when that 2700lb car moves like a little rocket
