Not wanting to talk for Brian, but the number of off region locos turning up at STJ was always large. Without looking up old Locosheds 6781/8 i would guess at being Tinsley/March locos, always common at STJ and further West (Pengam dock line of happy memory) Lots of steel trains needed lots of locos from both ends, also look at the 3 LMR type 2's , 5228, 5268, 5264 turning up. The Cardiff lads would frequently bike (not up to that at my age now ) drive ( if you knew someone with a car, or even splash the cash for a ticket to get there on weekends for a look round ( the natives were always friendly ! )
As the 70's moved on the number of foreigners arriving moved upwards, STJ could and did get anything from anywhere turning up, the only things i never heard of were Scottish type 2's and 73's ( well, the latter stated turning up after privatization and we know that a Scottish 26 got rebuilt at Canton !
John,
who has just found out that the Canton footbridge is no more :-(