I warn against soldering O2 sensor cables. I did it once because I did not have a new plug (I can really solder). It did not work, the values were wrong. During soldering there is often a too high contact impedance. Since then I only use mechanically pressed cold joints for such sensitive wires.
But where I say this, I would buy the 4 O2 sensors, 2 each for up and down stream of the Ford Mustang. If the connectors are different, you can take the old ones and connect them cold pressed.
If even the instruments and the unchanged ECU are taken over from the Mustang into the Morgan, one can do nothing wrong in this way, because nobody could or wanted to change or even reprogram anything at the Mustang. I would blindly trust to just buy the Mustang parts.
