That is deffo a Kiravans swivel.
Wife is 5’8 and no probs. I’m 6’0 and no issues either. My ex colleague is 6’4 and his head used to touch the roof on the way to work-he was a little uncomfortable.
My ply panels are only 3mm thick and fitted with those hidden trim clips and the trim tool gets them off without breaking the ply if being careful. I have split the ply in one place, but a bit of wood glue and a clamp and it’s stronger than ever by the following day.
I made all my panels out of 3mm ply sheets myself with a fine toothed jigsaw blade-being a value-orientated Yorkshireman like yourself.
It’s not a big deal. Try to find someone who is removing those original hardboard panels and use those as a template-that’s how I did it.
On the floor thing, mine is 9mm ply, not had an issue in over 4 years. I’ve got Altro floor, was from a place near us that does roll ends and it’s stuck down with double sided tape.
I’ll find you details of the place for the Altro when you are ready to do it mate.
Always happy to pop over and give you a hand if you wish.