I have a large section of my website devoted to these meters. www.petrocollect.com
-----click on the next page-----then click on ECO.
I have restored over 550 of these meters since 1988 and I am the author of the "Air Meter Identification" book.
If you plan on restoring these meters I suggest you purchase a copy of the Service Manual that I sell. Others sell copies of the original Service Manuals that came with the meter, but these are more designed for the repair person. I have completely rewritten the manual and put it in order that you would use to completely restore the meter.
If you have any questions you can call me also: 314-427-3943