Does anyone know how much fluid goes into a 1989 635CSI A/C system? My system has both front and rear A/C

How much fluid? Do you mean lubricant/oil or how much refrigerant? Refrig is added to achive certain pressures dependant on the type of refrig used. Your system should be a R-12 freon system but could have been converted to something else. Check for the factory lable under the hood for fill specs or check your owners manual.