The question of converting metric to pounds has come up before, some saying you need a new calibrating spring. All I have ever done is put decals over the wheels and recalibrate the unit, it has worked every time.
Sometime during the 1970s ECO switched to plastic wheels. When they did this they also changed the color, making the plastic wheels white on black. Why they did this we will never know for sure, but I would guess is that they probaly hold up better. I again just put a set a decals on all the wheels on my restored units and changed them back to what they looked like in 1947.
You can't go by pictures of the older units also, for instance all the 1947 pictures show the ECOs with a black hose, but all the literature states they the unit would come with a Red hose.
I may not have covered every question some people come up with in my service manual, but my customers know that they can call me and ask questions.
Jack Sim

Author, 1st & 2nd editions of Gas Pump ID book, 3rd edition is now available at www.gaspumpbible.com
Air Meter ID book also available