>and I don't have the key!!!!

   Turn the unit with the rear facing towards you. Loosen the thumbscrews - then use a *large* flat blade screwdriver to lift up the cover about 3 mm over the lock position. 
   The inside lever goes only behind an edge of the case ... pry between case and rear wall and lift the case up a bit.  Then push the cover from the rear to the front.
   When you have it open: pull the retainer bracket from the lock assembly -
fumble it out and throw it away ...

Uses 85nS 1 or 2MB SIMMs

Zero wait state.

   The 50-021 uses a proprietary MFM / ST-506 controller along with a CMOS version of a MFM 20MB harddisk - and that's the only drive supported on that controller. The 50-Z uses the MCA DBA-2 controller ... usually they use ESDI-like auto-detection for the drive size and doesn't use any tables (104xx error codes).
   The 50Z-BIOS however has an "AT-style" table for the MFM drives, which ends at Table ID 33 for the 30MB MFM-version of the MCA DBA-2 (17xx errorcodes).
   This table can be edited for larger MFM-drives (up to 500MB) with correcting the CRC checksum of the entire ROM pair. Did that long time ago for a Mod. 60 to install a 350MB MFM drive. Basically you can forget that stuff.