The system in SA wasn't as tight as it is now, period mods were OK and so was LPG. Unfortunately the system was abused and they clamped the rules down to stock only.
I am planning on getting the FC Wagon on Historic Rego one day, that's why I swapped the extractors for a standard manifold. Even the alloy rocker cover has to go
CD players are OK as long as they are discreet, no doof-doof systems.
Electric wipers are OK too.
At the end of the day it really depends on the inspector's interpretation of a modification. Probably more to the point it depends on the Police's interpretation of mods, because there are stiff penalties for the owner and club if you get caught in a modded car on Historic Rego.