Hi there,
Welcome to RChat and the Australian board...
Some time ago, I looked up information about a George Ham and Baulkham Hills for another RChatter... and tomorrow I will hunt out the info for you... but it's nearly 10 pm here.
I recall finding him on NSW musters out on a farm and also on the 1828 NSW Census. I think he had a son also named George, so perhaps that may explain the two different dates you have found ...
Here's the link to the NSW resources that RChat has on this board .... If you decide to get the certificates for those two deaths, please do consider purchasing the transcripts rather than the certificates themselves, as they have the same information at around half the cost.
Here's the NSW resources thread
http://www.rootschat.com/forum/index.php/topic,369703.0.html (several pages of very useful links)
and here's the BDM information from that resources thread...
Registry of BMD New South Wales
http://www.bdm.nsw.gov.au/familyHistory/searchHistoricalRecords.htm· Details on ALL Certificates for New South Wales
http://www.bdm.nsw.gov.au/familyHistory/certificateDatesAndContent.htm
http://www.jaunay.com/bdm.html
Transcription Agents
http://www.rootschat.com/forum/index.php/topic,300394.0.htmlI will try to help further, but it will be tomorrow or later ...

Cheers, JM