During the later years that the ECO was made they didn't put ID tags on them. If you send me some pictures of the entire meter and including one of the rear with the cover off. If there is an inside cover, remove that also.
You ought to take a look at my website, there is over 12,000 petro related images and a very large section on ECOs. I have personally restored over 500 of the Model 90s in the last 30 years.
Jack Sim jhsim@petrocollet.com
Author, 1st & 2nd editions of Gas Pump ID book, 3rd edition is now available at
www.gaspumpbible.comAir Meter ID book also available