Hello Ian,
I am wondering, from where did you buy this parang ?
Regardless of the age guesses we can make, it looks like a blade that has faced long extensive use.
Also the scabbard looks very used. lot of patina.
The original carrying strap has surely been replaced by simple rope because someone was in need to carry this parang.
The blade has decorations on the back. are these brass inlays ?
I think that cleaning the blade will give us a better idea of the quality.
However, personally I am not very much in favour of cleaning such a blade with the main purpose to convince others of the age or quality of the blade
Maybe you can give it a gentle cleaning trying to give more life to the decorations
I like this parang, regardless the age.
It has a history in Borneo, maybe much more fun to own than a jimpul with history in a museum
Best regards,
Willem