A 600 hp Mopar engine is easy to build and not all that expensive. 440 block, 4.25 crank, 7.10 rods, 10:1 pistons, TF 240 heads, TF intake and a cam in the 250 range. So that is the easy part. You'll have to spend some money on the transmission to make it safe and reliable and you'll need a Dana 60 or something equally strong out back. After that it is just power to weight ratio and some suspension tuning. A Holley Sniper setup makes 600 hp more streetable since you can easily program a street tune and a race tune.