72-450 desert master center cases

Need some help. Have a 72-450 (WR)desert master with a small crack on the high pressure side of the case from when the past owner rebuilt the motor. I have found some 72-450 CR cases and am not sure if they will work because of the different transmission gears and gearing. The CR came with a gearbox with one less speed than the desert master and I need to know if anyone knows if the cases from the 450CR will work on the 450 desert master (WR).? Thanks for any help!!