Since the Volvo 940 had to stay for a while and the head was worn out and it was using coolant I bought another B230FK and installed it with the help of my father.
Unfortunately back then the new motor did not want to start and we ran out of time. So we towed the car to the local garage for them to finish it. Borrowing my fathers car to get home was not really a downside.
The garage could not find the fault via OBD. Thanks to the Volvo community and Ben from Tinustuning I concluded the flywheel orientation must be wrong. I aligned the top dead point notch with the sensor but it should have been about 60 degrees before that. Disassembled everything, changed the flywheel position, assembled everything again and the motor ran!