722.6 is the 5-spd auto, still being used in the most powerful AMG cars. 722.5 was basically 722.3+electronic overdrive, while 722.6 is an all-electronic 5-spd with three times the torque capacity of 722.5 - 722.3 is incredibly rugged, but the OD forced MB to derate 722.5
The W210 and W140 introduced the 722.6 with the M111, M104, OM602 and M116 and M119 V8s, so it's in theory an easy swop. Just figure out how the engine signals differ between W123 engines and these later ones.
No, I don't think the OM602 had electronic injection, so the tranny can communicate to an all-mechanical diesel. But I may be wrong, I have been before.
And no, I would always
fit a manual tranny instead. My next dream project (you know, after converting Donkey to a 4Matic
) is a W123 230E with the 2.3-16 engine and a 6-spd manual from the M111. And, since "D
onkey" uses d
iesel, I shall call that beast with its p
etrol engine "P
ferd". Oh yeah
Sorry, my bad, off-topic again...