only the big gas 6.4 is the same block as the hellcat. the only difference is the hellcat block is orange and the truck block is black.
you can buy a new bge block for 1295ish as i did. buy a stroker kid to make it either 411 or 422 cubes. custom cam amd vvt locked out will be over 500ft lbs and 500hp. witb 20mpg plausable depending on cam.
also the 6.4 heads can be bough new but with cast valves for 1500 a set no.core charges. is what i bought. same as hellcat there as well besides valve material and intake bolt pattern is same as 6.1/5.7/6.4. out flow the apchies to boot by 10cfm across the board.
