The last new locomotives for the Rhymney were ordered in February 1920, about the time when serious planning for the grouping started in the Cabinet (https://discovery.nationalarchives.gov.uk/details/r/D7735748). Four were delivered by Hudswell Clarke in July and September 1921, and six from Beyer Peacock in December. They were slightly different in detail from the pre war R class. The classification AR doesn't seem to have ever been used in practice or officially but was certainly present on a Beyer Peacock drawing which is still in existence and available from HMRS (https://hmrs.org.uk/hmrs-22702--0-6-2t-class-r--12ft-6ins-driving-wheels.html).
Seven of these ten never received GWR boilers and kept Rhymney boilers to the end. The sketch is based mainly on the Beyer drawing, with reference also to WRRC drawings and to photographs. Very unusually I had enough information to sketch the inside valve gear: its a shame its almost completely obscured!