AI never operated non-stop betweem SA and India. The flights were operated BOM-DAR-DUR-JNB.
Also, MAN was served through FCO - the routing was BOM-DEL-FCO-MAN.
When AI served LHR with A310s, they routed MAA-KWI-LHR
The longest sector AI has operated with A310 is probably DEL-KIX (operated briefly right before the HKG handover when HKG traffic warranted its own 747 rather than a combined DEL-HKG-KIX flight).
Also, AI has operated BLR-PER with A310s (for less than a month - the service was then modified to BLR-SIN-PER). Not sure if that is longer than the DEL-KIX route.
"The A340-300 may boast a long range, but the A340 is underpowered" -- Robert Milton, CEO - Air Canada