507 is seen on my first visit to Porth depot in 1970, just less than a year old. The original service number for the Cardiff to Treorchy via Ystrad service (121) looks odd on these Atlanteans as they were associated for much longer with those services when they were numbered 320/321.
507 has the fleet number on the front dash panel. This was moved on these Atlanteans soon after the Western Welsh takeover to their standard position on the offside, below the cab window and this was done without waiting for the bus to be repainted.
