Not sure if there is enough room on an 8 inch converter, but you could just transfer the balance weight itself from the old flex plate to your converter. Good welds required, of course. Then just run a new sfi approved neutral balance flex plate.
I can send you a template of a B&M 10242, which is correct Magnum balance, but it's supposed to be for 727 transmission. I don't have a torque converter for the 904 transmission I have to test for starter clearance. I don't know if it will have clearance in a 904 application. The B&M flex plates are a little smaller diameter for the 904, at least I thought they were.
