tufcj
You'd probably need a TF727 flexplate for a 360. I'm not sure the 998/999 converter has the same bolt pattern though. The 727 flexplate can be re-drilled to match the converter. Remember that the AMC V-8s are externally balanced, so the flexplate MUST come from a 360 or you will need to have it re-balanced.
Bob
tufcj