All MkII's had an X chassis code, and AFAIK the first one was an RX10. Note it is not related to the Corona, despite the use of the "Corona MkII" badge in some markets.
incorrect, the first mark 2 was an rt6x, they had R series engines, unlike the x platforms of the later models. the first mark2 came out in '7 or '68. they are based on the normal corona platform.