There are for the TF series of transmissions 4 different flex plates made.
11" OD WITH UNEVEN CRANK SHAFT MOUNTING holes
11" OD WITH EVEN CRANK SHAFT MOUNTING holes
12" OD WITH UNEVEN CRANK SHAFT MOUNTING holes
12" OD WITH EVEN CRANK SHAFT MOUNTING holes
Chrysler used both series of flex plates. If the car came with an 11" converter (either 904 or 727) they used the 11" flex plate, and if it was a 12" converter they would use the 12" flex plate.
From what I'm reading in your post you're having a problem mounting your flex plate to the crank. See the above and get the flex plate with the correct bolt pattern that your crank has.
I don't know what after market converter you've got, but we typically at our place we build our converters with the flex plate muounting pattern for the 11" size.
Hope this helps.
Transman