Hi,
I have an old truck body on a HX 1-tonner chassis. There's a link in my signature below if you want to see how I did it.
They work quite well as a donor, parts are cheap and they drive really well.
The only thing I have found after daily driving mine for 12 months is there is a bit too much frame flex between where your rear body mount will be and where your front tray/bed mount will be.
If you look at how those old Holden bodies are mounted you'll see that there is a body mount on each side that ties into the chassis upstand for the tray, and that the body is really beefy through that back half. They use the body to stiffen the chassis.
It would definitely be worthwhile building a bit of a K or X frame through the centre of the chassis before you get a body onto it.