Getting the quaddy set up right will help plus setting the dizzy right for the engine also.

But a 253 with a non overdrive non lockup converter auto in a 1500kg vehicle with probably a 3.08:1 diff won't be brilliant fuel wise. You could spend significant $ chasing 3 or 4L/100. Even if you do 10,000kM a year, saving 300L @ $1.50/L is only $450 a year.