Now that i think about it, your right, the Powertorque was the first time i beleive we saw the small plug at the end to change springs, but there was the early LM, where the hole fore the G4 Adjustment knob was simply no there, but the cap was otherwise the same (infact, some still had the stem that stopped the knob from slipping)
I know there wers series 80 Engines fitted with G4 Carby's, and quite a number of them, so maybe 81 or 82, i will see what i can find out, and try to lock that date down a little more.
