R413a

Not knowing much about this refrigerant i hope toask a question.I have a chiller cabinet at home which is on R413a , theres no name plate on the compressor so i presume it was on R12 at one time . The problem i have is thet the compressor motor has locked so its a new compressor job but i was wondering if i could convert this to a R134a compressor because i have one spare.I know there both on P.O.E. but is there anything that i have to change also ? e.g. capp size and lenth ? or drier size ? Or am i best just ordering a new R413a compressor ?
thanks for your help , much appriciated.