I've now managed to get the names and letters (C, D, E) of the 3 partitions on the HD the same on both OS's. Good.
The external drive that was previously lettered the same now has different letters and WON'T allow me to make them the same.
The Floppy drive remains A on both OS's.
When I tried to standardise the CD-ROM & CD-R/W drives, I just created icons with '?' in red (on one OS only) for, presumably, fictitious drives. I've had them before and they stick around forever!