Daughter needs Gas mileage from 273 commando

All mods I could do to the suspension and Brakes have been done,Convertible sebring seats with shoulder harness, collapsible steering, full Firm Feei suspension ,Stage 3 power box, Right bore M/C, smaller W/C on rear to help with lock up, prop. valve , new run flat Michelin tires. Lets don't get into this...... I have driven myself nuts over this having to explain myself for letting a younger person drive an "Old Car". I say this just so "IT" does not rear it's ugly Head (Horse talk )and start running off....I love my child, it will be safe. LOL ! I just need your knowledge on better Gas milage....this is a new area for ME ! Ha Ha. Any more engine mods I can do to help? Thanks all for your replys, got to get back to work, Break is over......Tim:D