I am a bit surprised no one questioned the irregular intermix shaft in the Constellation. This is my attempt to accomodate the vertical core with two rear-stretching tubes in "Peak Perfromance" while also maintaining the decentralized feel of my Constitutions. My notion is that the horizontal V tubes would reach back to the two deflection crystals. The Constellation would still have nacelle reactors.
I always thought that the warp core we have seen on the Hathaway is a newer one the Constellations were refitted with, and I like to place it where the impulse deflection crystal was on the Constitution-class part of the saucer section.