You are most welcome, Dante.
The hard drive is an external drive although I wrote the files in a Macintosh PLUS (1987)
That sounds like a SCSI drive, and SCSI has not been supported for a long time. See if this illustrated Wiki article helps you determine if its connectors are SCSI:
https://en.wikipedia.org/wiki/SCSI_connector
If it is SCSI, this is going to be difficult unless you or someone else has a much older Mac with that interface. For old Macs without SCSI but WITH PCI slots, there was an option of a PCI SCSI adapter card, but none of your Macs have such slots.
I see a few direct SCSI-to-USB adapters but most seem to be the special 36-pin version used on SCSI printer ports. Most SCSI data drives are either 50- or 68-pin.
A few old SCSI drive enclosures had external SCSI connectors but the drive inside was ATA/IDE. Were this the case you could remove the bare drive from the SCSI enclosure and connect it via USB to a modern computer to recover data using a bare drive adapter:
https://eshop.macsales.com/item/NewerTech/U3NV2SPATA/
Does the Macbook Air have an older version of Office installed? Sometimes with Office, if a file on an older format will not open by double-clicking the file, you can open it by first launching Word and then using Word's Open... command. Sometimes.
You can ask around, especially of Universities. Some may have old lab gear that could read SCSI drives if that is what yours proves to be.
I'll check back later in the day to see what your have discovered.
Cheers,
Allan