Have your shop replace the races in the hubs (1 on each side of the hub) & what Supercuda said, have them also remove the swedge to seperate the hubs. dont add a prop valve right now (it is alot of fabbing, avoid it if you can & likely not needed) , I had 76 A body (2.75) single bore discs on a 65 dart with 10" rear drums & NO prop/braking issues with the OE splitter that you have. here's my rotors (SBP & BBP) for upcoming projects. You have rotors that will fit those hubs?