Multicam edit of an exiting sequence

Is it possible to create a multicam edit from an already edited sequence?

I have a 30-minute sequence filmed on 3 cameras. They are already synchronised.

I did a basic edit on the whole pile of synchronised clips to get the structure of the output and now I want to go through and switch between cameras without selecting each clip, but using a multi-cam sequence instead. All the online tutorials refer to only one clip per camera.

So:

I have a sequence with several video tracks. (Image attached)

The clips are synchronised.

They are all piled on top of each other in the timeline.

I have edited the pile of tracks so that I have the layout and order of the output - I viewed only the top track, although the other, synchronised, tracks are under it and I edited them to match.

So I have an edited, multi-track sequence.

Is this possible to create a multi-camera edit from this sequence without exporting each edited track to a new file and using those for the multicam edit? ... or do I have to export files of each edited track?

Does that make sense? I attach a screen-shot to help explain.

Thank you.

Johnny