To my knowledge the most obvious indication of a South African built truck was small white reflector lenses fitted to the front fenders,and of course right hand drive,other than that i'm at a loss for more info.
Just came across this thread and thought I'd better put you mob out of your miseries.
You got it all back to front

.....HOLDEN was
not exporting CHEVROLET trucks to South Africa at any stage. General Motors America exported CKD kits
(chassis/driveline only-no bodies) to Australia that were then assembled and their bodies then built in Australia by HOLDEN
It is because these bodies were built R.H.D. by HOLDEN that they are quite different to any model ever made by CHEVROLET. Just look at the HOLDEN body on my 1936 Pick-up and you will see it is nothing like the 1936 CHEVROLET made in the U.S.A.
(Just like some GMC and Maple Leaf trucks!)
Do a bit of research and see how many different bodies HOLDEN actually made from the late 1800;s through to the 30's and 40's before General Motors Holden (G.M.H.) was formed.

Bob.