Hi,
when i start to work on refrigeration,decade ago,i work with this tipe of units,use like refrigerant CH3CL, i dont know the English name.Sorry.
If You change the mineral oil with a sintetic one,and charge the units with R134a the units come back alive again.Change the belt too.Clean the condenser coil with compressed air,add a new paint and Welcome in the 1950!
If You change the oil each year,and the units have a proper maintenance,its all the chances for the units to live more then a human.