(1) Gains resulting from a liquidation pursuant to IRC 331 through 337 are taxable to the liquidating corporation to the extent these gains are attributable to corporate or individual share holders not subject to tax. In the event the liquidating corporation has some shareholders subject to tax in Montana and some who are not, the portion of the gain on liquidation taxable to the liquidating corporation will be determined based on the ratio common stock owned by nontaxable shareholders bears to total common stock issued and outstanding. This applies to all tax years beginning after December 31, 1980.