8 3/4 rear casting 1820657

Your rear center section is a C body unit only.YES some one installed it from a big C car to replace some gear set that went south.Now you need to check out some of the gear set that you could get from 58-64 in imperials,new yorkers,300,etc to find the ratio,s that could be in there.Or just lift the car,block one wheel and a freind with some brains,turn the drive as many times as needed to turn the wheel once,making note of how many times the drive shaft turned to complete the wheel turning once,your ratio,mrmopartech