I may have reached the limit of my mechanical reasoning for the evening, but I noticed the following;

 

The shop manual lists a Left and Right hand valve rocker assembly. But looking from left to right on this spare set of heads I cannot see any difference between the two, nor do they seem to be marked in any way (other than the L and R) but that is on the tube and not the castings or shaft.  Subaru took the time to make a L Vs R assembly that was independent of the castings, but unless I am missing the obvious difference I am not sure why.

Edited October 6, 201411 yr by subarubrat

There the same. So are the heads and valve covers.

Right head has EGR tube fitting tapped.

Sure, but the castings are the same for the cyl heads.. The only published difference is the valve rocker assembly that bolts to the cyl head casting, those have different identities and are stamped only on the tube as being L or R, but have no discernible differences.

Sure, but the castings are the same for the cyl heads..

 

yeah but if you put the heads on the wrong side you will be bummed when you go to install the intake.  So it is worth making note of and checking before installation so you don't waste brand new HGs.