Yes its possible, my 1989 HJ60 having 2H 6-cylinder non-turbo diesel engine, 3980cc , 5 speed manual does 7.5km/l in city with AC and 8.5km/l without AC, best ever got 11km/l checked by refill on GT road from Lahore to Multan @90km/h without AC.
1KZTE is fuel thirsty engine although its has enormous torque, my friend having a 1996 surf with 1KZTE also get surprised with my full size truck mileage.
Toyota 6 cylinder diesel engines gives you surprising fuel efficiency coupled with reliability e.g. 1HZ, 1HDT, 1HDFT, 1HDFTE etc.