I have posted several times, here goes again
Buy a metric bolt, M14 x 1. 5 thread, about 4+" long
Buy a Dodge dually lugnut for the 80s trucks. It has an integral flange head and is for 5/8 fine thread.
Buy a metric deepwell lug nut in M14 x 1. 5. It shuld be threaded all the way through, and if it has a chrome tin cover, press or cut the cover off.
Auto Zone, etc. have them.
Assemble, with the dually lug nut flange to the head of the bolt.
The metric lug nut threads onto the bolt and onto the injector top. use the dually lug nut as a slide hammer. Put two fingers on flats of the nut, against the flange. The most elegant would be to saw off some of the threads on the bolt so it goes only about 1/2" or so into the metric nut, and use red loctite on it. you want to end up with about 3-1/8" of smooth shank on the bolt for the dually lug nut to slide on.
The above should cost you around $5-8, less if you find lug nuts in the boneyard.