While I have never used Delavan pumps, I have successfully used Shurflo 12v pumps with a By pass regulator. I am not so sure the Shurflo demand pumps are intermittent duty. They seem to last pretty long in continuous uses.
Calibration should be more consisted using a by pass regulator.
it is one thing to do a off label applications. It is total stupidity to post it on the world wide web and expect people to approve.
You can lead a Donkey to water but you can't make the Jackass Drink