What you have is a Fry 17 five gallon pump with a Rush conversion. That is why you have five measuring stops. The Rush pumps took a 12 X 27 cylinder. When you remove the adapter plate you will see that it takes a 10 X 20 cylinder. The Fry 117 takes a 13 5/8 X 22 cylinder. You can get reproduction parts to convert it back to an original five gallon pump. The top casting and Dome looks like they are from a different top than a Rush. Not sure what they are off of.