Your parts "are" inventory, any way you look at it. If you had no parts on hand at the beginning of the tax year, then your BOY inventory is zero. If you had no parts on hand at the end of the year, then your EOY inventory is zero. Since you purchased $300K of parts in 2016, "and" sold those same parts in 2016, your COGS is $300K. The first example applies if you just change the COGS in that example to $300K.
