G'day John,
Good to get interested in research. However like trucks it can be addictive. What REO does your son have? It is all capitalsafter the names of the founder - Ransome Eli Olds; so "REO". I am a member of REO Club of America I have a 1934/35 REO truck. Coach-built timber framed cabin with sheet metal tacked on to it.
I actually had Year 10 work experience at a truck repairers in Goulburn. I stripped down a Diamond REO cement truck. I would consider that sacrilege now - back in the 1970s it was fun.
Too far away from you and probably a later model as well, but back in 2015 Price Truck Parts were wrecking a Diamond T Accessed December 6th 2016 from,
http://pricestruckparts.com.au/diamond-t-truck. I have no association with the seller.
Kind Regards
Lionel