I have the early tall deck block - 22R.  That was my understanding too, that the pear shaped port was an RE feature and one way to distinguish the RE heads from the Rs.

Makes sense why the design change for IFS.  Hmmm...

But ya know, a lot of times things that were more expensive to make weren't necessarily better.  Such is the nature of engineering.  An engineer has a good idea, it goes to production, and later on it's determined that another, simpler idea works just as well if not better. 

Eventually I'll put my 20R head on this engine. The hybrid motor I built for my standard cab has a lot more oomph than this stock engine, and I never got rid of that restriction where the intermediate pipes come together on that truck.