For completeness an update.
I found the rattlegun loosened the harmonic balance bolt easily, so inspired me to continue.
I was able to borrow a claw foot puller to remove the harmonic balance.
Radum have them for around $9 and super dear around $33.
Harmonic Balancer Puller 13pc Set
www.radum.com.au
I was surprised how loose the belt was on the idler side, barely any contact with the belt at all.
Fairly obvious belt replacement, but did find a terrific utube on the subject that helped a lot
So water pump and belt replaced, checked welsh plugs ok etc.
Thanks for the forum help