IF the compressor is siezed you might consider replacement with a unit still in production.. They are all the same size, you may even be able to use the same "Lower" unit (if it is a ducted model this is the part that hooks to the ducts) and only replace the upper part and the inside "Grill" part. You may need to add a Thermostat, again depending on the model you get.
Noting major save lifting the upper unit onto the roof, that is a female canine of a job. Best done by 2 people or one very experienced and insured installer.
Nothin adds excitment like something that is none of your business
Kenwood TS-2000 housed in a 2005 Damon Intruder 377