Weird question this is.
You should have the disks (or adfs) for 3.1.4 as well.
Anyway, you will need a workbench.library on every bootable device you want to use with a Workbench, as it is not in the ROM anymore. But the ROM will kindly search for it everywhere and asks nicely if it cannot find one.
Maybe icon.library as well. Can't recall.