G'day,
your only issue as i see it is the torque converter (you have also mentioned it)
It is my understanding that the C4 has two bolt spacings for the torque converter.
If my memory serves me right its 10.5 inches and 11 inches.
Regardless, whichever you plan to use, the correct flex plate is available off the shelf, and the real experts will be able to tell you how to identify what you have, and what you need.
Cheers
Jas