73. In computing, at any particular time after 1971, the adjusted cost base of any capital property contemplated in section 68 that was owned by the taxpayer on 31 December 1971 and thereafter without interruption until that time, if the property was one of a group of identical properties owned by him on that date the following rules apply:(a) section 259 of the Taxation Act does not apply;
(b) where the property is an obligation, for the purpose of paragraphs a and b of section 68, its amortized cost to the taxpayer on 1 January 1972 and its fair market value on valuation day are deemed respectively that proportion of the aggregate of the amortized costs to him at that date or of the fair market value on that day of all obligations of that group that the principal amount of the obligation is of the principal amount of all the obligations of that group;
(c) where the property is not an obligation, for the purposes of paragraphs a and b of section 68, the actual cost or the fair market value to the taxpayer of the capital property is deemed the quotient obtained when the aggregate of the actual costs to him or the fair market value, as the case may be, of all capital properties of that group is divided by the number of capital properties of that group; and
(d) for the purpose of distinguishing any such capital property from an otherwise identical property acquired and disposed of by the taxpayer before 1972, he is deemed to have disposed of the properties he acquired at a particular time before acquiring another property after that time; likewise, for the purpose of distinguishing it from an otherwise identical property acquired by the taxpayer after 1971, he is deemed to have first disposed of properties owned by him on 31 December 1971 before acquiring it.