I did this to a '68 Dart 2 door sedan back in '05, with a '94 ECU and a 360.
It was done with a 4 speed and hydraulic clutch.
Didn't get it QUITE all finished, but it ran and drove.
Offered to do modified harnesses (pre AND post 1996) for this, but no interest was expressed and I dropped it.
I will say this, use the stock fuel pump from the '99 and hang it from the inlet fuel line, then drill a small hole in the sending unit for the power wire (red wire) to pass through and seal it with Quick Steel. Ground the pump using the fuel inlet line and a clamp, then properly ground the sender on the outside.
MANIFOLDS: The passenger's side Magnum manifold will fit a '67-'76 A body, but the driver's won't fit w/power steering, as the box is too bulky, even tried a Jeep Magnum manifold and no dice without a LOT of grinding.
I ended up with a pair of the earlier, '67-'73 style, 318 A body manifolds and modified the passenger's manifold for the '94 Magnum's EGR tube.
The key to the wiring is the switched power side of the alternator, which is a blue wire, runs the power for the whole system. That wire is also tied into the hot side of the injectors, which is a green wire with an orange stripe and also ties in with the PCM switched power, which is a crimson colored wire.
The "Check Engine Light" is a black wire with a fuchsia pink (really!) stripe.
In truth, I threw away nearly all the wiring, from the bulkhead connector into the dash harness, because It's worthless.
In the end I used the stock gauges, their original wiring and sensors and whittled the engine/PCM wiring down to engine management, though using the PCM's voltage regulation circuit is a wise move, but it too can be bypassed.
Quoting the Terminator: "...I Have Detailed Files..."
Mark.
