It took me a while to get all the material, but i have finally modified the TF-322.
As you guessed, my "old" 3.5 mm port won't fit so i organised new ones and followed your advice to make pigtails. I soldered a part of the belden cable to ground, handshake and data of the TF-322 and now the first cable is ready and working :-)
TF-322 - modified.jpg
thank you very much Jeff !
I now have only the second part left, to connect the first flash with the second one. I finally found some old SC-19 cable and will solder the the 3 pin plug to one side and on the other end another 3.5 mm jack plug.