It is easy to make a restriction in a Fitting.
Fill about 1/4" of the end of a Fitting with JB Weld Epoxy and let it cure properly and after that you are able easily drill what ever size Hole you want into the Epoxy.
See Post #3 for the test specs.
Correcting low internal IP fuel pressure on my 85 300D turbo
If you are going to do the test it is best to do so with a New Fuel Filter so a plugged Filter does not influence the test.