Also a major determining factor will be the intake. You mentioned wanting to " run a long crossram 2x4" on the 392. Chrysler never made them for the 392, only the wedge engines and the intake port spacing between the wedge and early HEMI are completly different making it virtually impossible to adapt the mainfold to the HEMI.

If you build your own or if an aftermarket one was produced a lot will depend on how effecient it is.