Good to hear of another prodigal railway modeller. There is no reason why you can't have sessions on different days for running Irish and BR stock on your layout. Especially since that real life issue of track guage can be ignored.
Good to have a close look at the latest version of the Dart at the show in Blackrock today. It is an impressive model with special features such as the arcing pantograph.
There has not been a finished model made of the E class but there have been two kits. The first was by Fanfare Models (later released by Ryanbus) and the second by Jim Poots. Neither would be available now unless found second hand.