Interesting that the Morton's bus to/from Terminal 2 (Stena Line) is no longer free. The fare is €2.50 adult single from the terminal to Connolly and Westmoreland Street with an option of a €4 fare to be dropped off at Heuston. There is however no pick-up at Heuston (or Connolly for that matter).
Further details here:
http://www.stenaline.ie/ferry/rail-and-sail/holyhead/
So, a passenger wishing to use the route 53 service bus to/from Stena Line (Terminal 2 - adjacent to the top of Terminal Road South) could either use the stop at Terminal 1 (Irish Ferries & Isle of Man Steam Packet terminal) or use the stop at Alexandra Road/Breakwater Road South (stop 2269). It's around an eight minute walk from either stop to the Stena Terminal and in terms of footpath continuity/the need to cross roads the walk between the stop at Terminal 1 and Terminal 2 is preferable.
Incidentally there is a Dublin Bus pole still there opposite the Stena Line terminal (stop 2254) which was where the 53/53A used to stop before the road layout was altered a few years ago but it would appear essentially impossible for the revised route 53 to serve it due to the road and traffic island layout.