I don't know why this popped up in Project Guidance today since the last post is Aug 23...
Thought I'd add to the topic while it's up: If you want to improve fuel economy on an older petrol car like this don't bother with fancy electronics and displays. Buy yourself a vacuum gauge, plumb it to the intake manifold and plop it on the dash panel in plain view.
As you drive, do whatever you can to keep the gauge needle pointing as deep into vacuum as you can. Some vacuum gauges will even be marked with an "economy" region:
Keep the needle in the green.