'68 318 to carbed Magnum 5.2: Check my checklist

Do you really want it to flex? I don't... My brother and I used a B&M flexplate on his cast crank ('73, therefore external balance) 340, and it worked perfectly fine. Lots of people use them on their engines...and although I'll cop to not knowing that many people in the world, those with an aftermarket flex plate are happy with them.

EDIT: just saw your want ad...good idea