The Mini MK2 steering arms were designed to be used with the later model rack that has a tighter turning ratio than the early MK1 rack. A pair of Cooper S thicker arms can be purchased cheaper than a single arm. The angle of all arms from 1967 are slightly different thus allowing the tie rod end to have a little more range of adjustment into the rack. An alternative is the thicker upgrade arm as used on Cooper S and 1275GT. See
BTA894 and
BTA895 which should be fitted in pairs.