You cannot have an actor as a visual. But nothing stops you from spawning a furniture actor at this point and trace to position it (the visual widget can be invisible).
Check this out:
This can be made much simpler if you do not need a drag visual widget at all.
Pass Unhandled during onMouseDown → Spawn an actor and send its reference to the PC (or, better, call the PC and have it spawn actor from class) and start tracing.
The widget can use screen position to trace but it can be cumbersome at times. Better have the PC handle that.
One reason to do it in widget is when you need to drop the whole thing onto another widget. But that’s not what we want here judging by the description.