If an amount is required to be included under section
423
(c) in gross income of the estate of the deceased employee or of a person described in paragraph (1), there shall be allowed to the estate or such person a deduction with respect to the estate tax attributable to the inclusion in the taxable estate of the deceased employee of the net value for estate tax purposes of the option. For this purpose, the deduction shall be determined under section
691
(c) as if the option acquired from the deceased employee were an item of gross income in respect of the decedent under section
691 and as if the amount includible in gross income under section
423
(c) were an amount included in gross income under section
691 in respect of such item of gross income.