Form follows function.
Since the 250 DMUs have been mentioned let us look at the functional requirements:
> Each vehicle about 25 metres (75') long
> Diesel powered,
> Twin engines for reliability because a single unit may be at an isolated place on the system and has to get home.
> Air conditioned with auxiliary diesel generator able to power two cars
> Able to run in all combinations of single and multiple unit consists.
> Driving stations at each end for total flexibility
> Providing step down vestibules for low rail level platforms.
About that point the similarity with the Budd RDC ends. As cars they followed the pattern developed by the SAR for the Overland Cars.
The power train was completely difference to Budd RDCs
NSWGR bought their Budd RDCs and then tried to meet the same function with the ill-fated Tulloch cars
Victoria followed years later with the Sprinters which have the same function and therefore follow the same form; I understand they work well.
Too much Christmas pud has made me a mite tetchy.
For the size of its system, probably the smallest route miles of any mainland state, the SAR designed and built in its own shops more of its diesel fleet than any other system.