Finding records of a C.M.H Recipient?

Near the end of ww2 my Grandfather who was 2nd A.I.F, was involved in a combined action with some American troops. Some family say they were marines some say they were army, Pa never really talked about it. The upshot is that a young man named Julian Van Noy (not sure of spelling) stayed out in an exposed area and was cut off and killed, I new he was posthumously awarded the CMH and that he was on of the youngest to be awarded it but what I wasn't aware of was that my Grandad wrote a letter to his parents that was later used in evidence to make the award. My Aunty has his old war diary which she won't let anyone look at and I was wondering if there was any chance things like this were kept recorded and if so would I be able to obtain a copy somehow. Simply to get a bit of an insight into my Grandad who was my hero but I learnt more about him at his funeral than I did during the 35 years of life that I had with him. The action happened on Scarlet Beach in a place called Finschaafen on the northen coast of Papua new guniea. I would be most grateful for any help.