Today, the pinout of the 40pins connector was checked. The inverter was powered up at the DC side through a isolation transformer and the voltages on the pins checked. The pinout of all the daughter boards were determined (communication and LCD daughterboard), as far as possible. The size measurements of the Logic board were taken for a new PCB design.  See Github for the latest information. 
It will be possible to reuse the LCD board and the isolated RS485 communications board, which is great.

In the end, it will be easier to recreate the Logic board then to reuse it. As you need to buy a special programmer to be able to program the DSP, and this programmer will cost just as much as a complete PCB design. And I much prefer the STM32CubeIDE anyways.