What about using an existing flexplate with no cracks and laying up a couple
layers of carbon fiber using the appropriate resin system?  You could
eliminate the lightneing holes and place the fiber in the weak areas?  The
plate would need to be sandblasted and cleaned to ensure a good bond.  You
could use faseners to secure it if you feel that the bond is inadequate.
Minimal weight added.

Joe Berki
Limo EZ