Do you plan to pull a vacuum on the system before adding Freon?
Yes the Oil and Freon are mixed together.
If this were my car and the only thing wrong with the AC was the clutch, I would repair/replace ONLY the clutch. Hands down. Even if more expensive. This avoids all the issues with draining, vacuum, re-filling the system.
If replacing with a Ford Clutch, it's possible to retain the field coil and only replace the outside load bearing clutch. MUCH easier. In fact, just use the Clutch from the salvage yard unit and call it a day.
Also avoids any issues with contamination from a salvage yard compressor.
OBTW, the oil amounts quoted assume an empty system which yours is not. Remember that the receiver/dryer will hold the lion's share of the oil.
2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.