67 cuda rear end swap and front disc brakes...please help

thanks guys...anyone know the average cost of doing this?

That depends on what you pay for the used parts. The 8.25 rear could cost from 100.00 ( local 3.21 open ) to 500.00 plus for 3.55 suregrip.
Most who change out the front brake assemblies will go ahead and renew all front suspension components at the same time. 600.00 all done is my guess for an average.