A-Body 8 3/4 Backing Plate

If he has a stock 8 3/4 with 4 inch small bolt pattern axles (OP doesn't specify) he will have to have actual factory 10 SBP backing plates. 10s or 11s from anything else will not work because of the difference in axle offset. If he is using BBP aftermarket axles or cut down B/C/E axles he will need the NON a body backing plates in either 10 or 11 inch.