The one feature that I really enjoyed in Directory Opus 4 was the small vertical drive / device bar in the bottom left corner that had a scrollbar
attached to it. Can someone instruct me on how to add this to Directory Opus 8 or is this not possible?
You can do this, although instead of a scrollbar you'll get a >> arrow which pops up a sub-menu containing any items which don't fit.
Go to Settings -> Customize, then the Toolbars tab and create a new toolbar. Click the Vertical checkbox and position it where you want it in the lister.
Next go to the Commands tab in the customize dialog and, from the Go category, drag out the Drive Buttons command. This will turn into a list of all devices when you exit customize mode.
You can adjust the Drive Buttons command so that it does/doesn't display icons and labels for drives, and also so that it shows/hides certain types of device or explicit drive letters. See the manual for details and ask if you get stuck.
Check out the Toolbar Editing video tutorial which demonstrates many of the steps above and will teach you a bunch of other things as well.