657.3. Notwithstanding any other provision of this Act, where a taxpayer acquires a right to or to acquire an interest in a trust, or a right to or to acquire a property of a trust, and it is reasonable to consider that one of the main purposes of the acquisition is to avoid the application of section 657.2 in respect of the trust, there shall be included in computing the income of the taxpayer for the taxation year in which he disposes of the right, otherwise than pursuant to the exercise thereof, the interest or the property, the amount by which the proceeds of disposition of the right, interest or property, as the case may be, exceeds its cost amount to the taxpayer.