When I first swapped injectors to work on my 550 tune, I opted to swapping rails.  The EJ25D rails will fit in place of the stock EJ20G/EJ22T rails and accept phase2 injectors straight away.  They can be found relatively cheaply from a junkyard, but are slightly more painful to install.  At some point, I needed to swap back to the stock gray injectors for work on the 440 tune and decided to go back to the stock rails and use Carl Davey's adapters.   After that,  for ease of install and only a small cost difference, I have recommended using Carl Davey's adapter for years.  Carl decided to fold up shop and that left only DeatschWerks kits (at a bit more of a premium) as a viable alternative.  There was a shop in the UK that got the rights to resell Carl's kits and I had worked with them with the hope of providing a US resale channel.  After a trial of about 5 kits, the communication broke down and I was unable to source any more to resell.  I finally took it upon myself to make up my own adapters and enlisted my ME friend to help CAD up the design.  After a few 3d printed prototypes I found an online machine shop that could produce in medium quantity at a good price.  Due to the inherent danger of working with the fuel system, installation should only be done by a qualified mechanic.     

Enjoy!