Original photo date of June 1968 is suspect since small yellow panels were introduced in 1962 and although the SR were slow to apply FYE, surely something would have been done long before this date. Robert Gregory adds D6538 was converted to a class 33/1 in June 1967, when it gained BR blue livery with full yellow ends, but retaining the four digit number. It went on to become 33118 in 1974 when it gained its TOPS number. My research suggests that it retained green with no yellow ends right up until the conversion was carried out. So the 1968 date is probably wrong, but it could have been as late as 1967 the quoted date of June 1968 is probably June 1966