So here is what I have in summary based on everyone's input........
* Shut off solenoid (electric shut off = ESO) is reliable and rare to fail.
* Solenoid operates with the cold advance solenoid within the housing and is cooled with diesel fuel in a low pressure of 3-4 psi compared to 350 psi in the pump itself.
* Not a good idea to simply cut off the fuel supply as this would starve the IP and also lack cooling to the solenoids.
* Solenoid is fed with 24V from the control box when the run switch is activated. While the solenoid is energized the fuel is in 'on' to the IP.
* there is a reverse ETSO solenoid that when activated will do the converse and shut off fuel off at the level of the IP. This is better as it doesn't starve the IP but it does requires power to shut of the engine.
* If the ETSO fails you will need a backup such as cutting off fuel with pair of pliers or a switch.
* Advantage of conversion is allows engine start regardless solenoid condition and disadvantage is the work involved and having to add a way to cut off fuel or carrying a pair of pliers to pinch the feed or return line.
After reading all that I have regarding this thread and IP's, here are the things I take away.
1, Stanadyne makes a LOT of IP's and they are used in many diesels. The majority of them use ETR for a reason.
2, In the PDF they show a manual override for the ETR
3, If I were ever so inclined to have a backup in case of a solenoid failure, it would be a simple mechanical version that retains the ETR