Yes, sounds like 1.5 ton. 1 inch equals 2.54 cm. I mm equals about .040"(.03937). Those tires are probably 20" at the rim. The bolt pattern is common and is called 5/10, which has been used up through the '90's at least, although with a slightly larger hub diameter. So, in the 'States, at least, the first use of tubeless tires in the late '50's, with 22.5" tires and rims, on farm trucks, mostly, will fit these axles with the use of a .25"(6.4mm) thick adapter ring.

So, I don't know what was imported to Oz, but if you find some 22.5" rims with that bolt pattern, grab them, they will bolt right up. Sort of rare in the 'States. 9 X 22.5 tires work well.

Ed

Last edited by EdPruss; 04/07/2018 1:51 PM.
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.