grose valley blue mountains Australia - help needed for planning

Hey guys,I am planning on walking from Govetts Leap to Yarramundi via the Grose Valley on the 20th to 22nd of Nov.
The distance is only about 55km and I have seen a fastest time of 15 hours (this was some time ago and fires may have cleared it out).
The NPWS guy at Blackheath said it may take us 7 days because of the thick bush and lack of path, River swims etc. (The guys had never done it himself and didnt know anyone who had recently)
.I have allocated 3 days ( will need to go to work the 4th day) and I was wondering if anyone had done this walk before as I can't find much info on in.
There is an exit 12km from the end but involves a long fire trail walk ( which could be done at night should we need to).Any info on the walk would be appreciated.
Thanks Dave

Wentworth and I have also been planning this one as well but went for a Kowmung river trip trip last week instead as it was more remote(Keep eyes open for the upcoming TR) I hear that it is tough going as the regrowth from the fires a few years ago has scrubbed everything off. Also there is a pretty good reason that they call it the devils wilderness through the harder part! With all the rain as well the river will be pretty swollen. The Kowmung was moving scarily fast in parts with heaps of sweepers that would make a experienced canoeist cringe let alone a cascader or li-lower. I think I would allocate one more day in honest only to relish the splendor that is the grouse river valley
Would be a trip for the memory bank though.