Hi jensshed!
I've tried to find an accurate answer to your question on the GVW of your truck and can't come up with the exact number. My guess is that it is not more than a 1 1/2 ton. Looking back in the specs book for /46, that's what it shows. But!! I found a site (see below) that shows 1936 1 1/2 tonne and 2 1/2 tonne trucks in Australia. By their appearance, they seem smaller than North American vehicles rated as that, so it's possible there is a different rating system in Australia. Just a guess. Regardless, these are old 'gems'. Hope you get your engine fitted OK.
Cheers, George
http://home.vicnet.net.au/~oldsclub/36hist.html