ERF:
This one is…Chassis 18019 (R&D)
Model 6.8.GM (R&D Exp.).
Cab - 4MW/2 type 43756 (JHJ Exp. spc floor).
20’ 9" wheelbase.
Despatch date - 8th August 1969 to Australia.
Engine - GM 6V-53N (42993 6D).
Gearbox - MT41 (40636) No 5265.
Clutch - Not recorded.
Eaton single drive axle.
Axle - Eaton 18700 ratio 5.57:1
Hendrickson bogie.
Balance beam assembly not fitted.
CP front bumper fitted.
Wow! Nowt like actual information, is there? 
This could be the vehicle that 3300John remembered. IIRC, he said it was about the place in 1967 (before the first production MWs), and the build sheet says it was an R&D chassis.
The vehicle is no road-train tractor unit, as one would assume(!). It is single drive and the engine is only a tiddler, not an 8v71. It would have been better off with a 6LXB! What was ERF Australia thinking?