Interesting stuff @Mol_PMBand @Horsetan thanks. Just realised that from photographs of 558 I may only need to bother with tank side numbers as by late 50s she had no buffer beam nos!
Irish railways had basically abandoned railbuses by the 50s as outdated technology, preferring more advanced designs such as the Walker railcars. BRs adoption of the concept seemed a rather retrograde step.
As one who recalls both in service , the AECs were a good design allowed to fall into decrepitude. The Pacers were a bad design allowed to go into production!
The 5 LEVs, of which RB1 was one, played a part in the genesis of the Pacers. One of the LEVs is apparently still in Ireland, part of the abortive UK gauge line near Dundalk