I've helped a few customers with 'Cuda's with the same goals as yours. This is the direction I push them, but this is just my opinion. I always recommend the Gen 3 swap versus trying to build the "old" engine that is in the car. You can get a complete VVT 5.7 395 HP truck engine for around 2K. You can't build the old motor to 400 HP for half that. MS Gold control for $1200, and your done. You'll need engine mounts, retrofit fuel pump and lines, etc.., but still very reasonable price for the power and drivability your gaining. Next is the OD. Gotta have one! Manual trans is the easiest, TKO fits without tunnel mods and T56 will require tunnel/torsion crossmember mods. Automatics get more complicated. Nag's can be used, fit in the tunnel, but control is, well, not ideal, and they do not have a slip yoke, so $800 custom driveshaft with slip joint. Standalone systems are available for $800-ish to control the Nag. Now, I have recommended the 4L80E, and before everyone freaks out on the Chevy trans, remember the Nag is a Mercedes unit. Adapter is available to run the 4L80 behind the Hemi, control is available from everyone, it's a very good trans and holds 800 ft. lbs. stock. Trans will run you about 2K, adapter about $800, and control a few hundred. Suspension/brake upgrade are a must. For a driver, I would recommend the Hotchkis TVS over any of the K frame replacements. Brakes can be as simple as the later OE disc swaps or aftermarket hub/rotor/caliper packages.