rear drill and slotted rotors

I have a 78 firebird 10 bolt rear end in my 55 chevy. the willwood rear disc set up is a little steep for the drill and slotted rotors. If I have to pay that much for rotors, I will get a complete new set up - question is what will interchange with the rear end - I was told a 80-81 set up from a firebird?

are there any other set ups out there that don't cost an arm and a leg?

thanks for help