The 400 HP 318 specs are here.

One build made 400 HP at 6,150 RPM and 382 lb/ft torque at 4,900 RPM and the other one made 406 HP at 5,900 RPM and 408 lb/ft peak torque at 4,700 RPM. After all of the shouting and hype to sell magazines, NONE of those 400 HP 318 builds resulted in torque figures as high as a basically stock Magnum 5.9 with just bolt-ons:

Mopar M1 single plane intake
Barry Grant Mighty Demon 750 CFM carburetor
TTI headers

The 5.9 produced 345 HP at 4,600 RPM and 426 lb/ft of torque at 3,800 RPM - more torque at an average of 1,000 RPM lower than both 318 builds.

Build a 360. Get a Magnum 5.9 as Patrick mentioned (easier to find) or even snag a 89-92 LA roller 360 block if you run across one. They are probably harder to find than the later Magnum blocks, but all of the later Magnum roller hardware interchanges, plus you have the option of using either Magnum or LA-style heads on it. Casting numbers to look for are 4315830, 53006921 and 53020006.