I took some pics today but mostly you can see only the bottom of the adapter and the filter.
If you look at the pics of the spin on oil filters you can see the same type of adapter.
What John has done is make an alloy adapter base which duplicates the original can sealing system. The original gasket simply is compressed by the alloy adapter, the original bolt at the top which previously held the can in place now holds the adapter in place. Then the adapter has a threaded attachment for the spin on filter.
Just as on the spin on oil filters you can see the advantage of a quicker change and better filter.
What is unseen, however, is the problem with the primary filter removal in the first place. The bolt holding the primary fuel filter can is reached from the top side where you cannot see the filter. I found I had to loosen the alternator, get it out of the way and then use a 1 inch open end wrench to turn the bolt to loosen the filter for removal.
The install procedure for the adapter install is the same as the original primary fuel filter can. Turn the top bolt to pull the adapter into position on the gasket and tighten. When you have a good seal between the adapter and the base, spin on the new filter.
Perhaps John can post a pic or two of the adapter, because I am for certain not going to pull it off!