Be careful what you get into on those, they were probably set up for R12.
What's wrong with the compressors? If they locked up, or the system has been open, it will need to be thoroughly flushed. If the old compressor shed metal it will be packed in the condenser. If it's a fin and tube condenser it will clean up, but if it's the vacuum brazed aluminum type they are best replaced.
Be sure to follow all the procedures as far as replacing the accumulator and getting the right oil and the proper charge. R134 is very sensitive to over charging.