I've been doing a little reading. The lockup converter needs an extra solenoid to supply it with more fluid to lock, so even if one were to source a lockup converter, getting it to work on the earlier trans would have to involve modification to the valve body, plus switches to control when it functions.

The 722.6 has a fairy complicated tcu with adaptive learning, self diagnostics, limp modes, etc... I always wonder at these though: if all the decisions are made in the tcu and the wires from trans to tcu just represent sensor inputs and jumpers to activate various solenoids on the output. If so, one could just ignore the sensors and create a manually shifted auto easily enough, which would be kinda cool.

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'82 300SD - Somewhere over 220k - Becoming reliable...