I'd be inclined to get the overhaul kit for the carb and rebuild it to the spec for a 79 DT175 production code 2k4 with the jets to suit and then go from there, esp as your paying for the bottom end to be done. With that airbox TBH it shouldn't run with a 160.
I have the later airbox on mine and that has a 160 main, i tried a 170 to allow for the pipe and a K+N and it just plain wouldn't run. It would start from stone cold and then just die out as it warmed up. Your talking about being over by far more.
I would bet you were running with a bad air leak, maybe a blown crank seal and the massive over fueling compensated to get it running. These engines are tough and don't die easy, they don't take tuning well but they can take abuse in spades, believe me i've given mine plenty. Thats why i think your bike was well on the road to terminal anyway.
As to the premix, personally i would fix the autolube system. It works incredibly well, is nowhere near as fragile as people think. They get disconnected because people have thrashed the bike to an inch of its life or run the tank out and its siezed (quel suprise) then blame the oil pump and remove/disconnect it (sound familiar). Chucking oil in the top of the tank, that just isn't as good.