These are some of the mods I did when I went from a 273 to a 383 in my '68 Dart.
Radiator, Twin electric fans $ Relay, .920 Torsion bars, BB Trans & TC, Motor Mounts & torque strap, Headers, Center sump oil pan (to clear K member), shortened drive shaft, 8 3/4 Rear end, Front disc brakes / metering-proportioning valve, Rear spring perch relocator kit for wider tires, Weld -in Frame stiffeners and new shocks, to name a few..