i dont think a 3CT can give anything more than 12KM/L on a Jeep. You must take into consideration the non aerodynamic shapes of Jeeps
3CT if used in car can give around 16-17KM/L depending the driving style...
for the kinda of Jeep you are having.. i suggest go for 2LT or a 3L (non turbo).. the reason is power to weight ratio.. CJ7 converted to wrangler weight alot!! a small engine will die down soon
a non turbo engine will give you better millage so 2L or 3L non turbos are ur choice
again if you get a 10KM/L average from a jeep.. ur lucky