I learnt to drive in an old IIA with a 186 redline in it. I averaged 15l/100km in it, including extended hwy work.
The engine was a stock 186 with Yella Terra heads & 350 holley carb. Driveline wise, stock gearbox and I had a high ratio t/c gearset put in by a mob in Toowoomba, buggered if I can remember the name of the place though. That made a huge difference and meant that at 100 you were pulling 3000rpm. Driveability was much improved.
I then added LPG to it and that returned 18L/100km. Provided the engine was given regular runs on petrol it was kept happy.

