Here's the salient point:
No matter what System version you run on a Mac Plus you cannot exchange floppies with an IBM machine without buying extra hardware. The Plus is equipped with the original IWM disk controller (used in the Macintosh 128k, 512k, Plus, II, and the first batch of SEs), and this controller is *incapable* of reading or writing MFM-formatted floppy disks. (And likewise is incapable of writing floppies which can be read on a PC equipped with a normal floppy controller.) And this applies whether or not you're running Apple File Exchange software.
In other words, to get data onto a disk readable in 400/800k only machines you pretty much have to have a newer Mac as a go-between.
No matter what System version you run on a Mac Plus you cannot exchange floppies with an IBM machine without buying extra hardware. The Plus is equipped with the original IWM disk controller (used in the Macintosh 128k, 512k, Plus, II, and the first batch of SEs), and this controller is *incapable* of reading or writing MFM-formatted floppy disks. (And likewise is incapable of writing floppies which can be read on a PC equipped with a normal floppy controller.) And this applies whether or not you're running Apple File Exchange software.
In other words, to get data onto a disk readable in 400/800k only machines you pretty much have to have a newer Mac as a go-between.