Thank you all for the feedback. I posted this topic on the Hipo site. If you believe the period Ford parts and cross reference manuals, up until some point in the 65 model year the axles for the all 8" and 9" used the same tapered axle shafts (Fairlane Carriers WCU, WDK, and Mustang V8 Carriers WCL, WCZ, WDT). That said, what do the best documented original 64.5 HiPO cars have? The beefier axle shafts can be identified by "C4OW" molded into the center hub, while the tapered are "C2OW".
-Scott