There is no "roll over" option in play here. If you sold securities and have a gain that's a taxable even irrespective on what you did with the proceeds.
As far as your cost basis question goes, your cost basis of stock you sold is the value of the stock on the date of death, (sometimes a different date, 6 months after the date of death is used instead, but the executor of the estate should have informed you if that was the case), and that's your basis for reporting gain or loss on your sales. You don't get taxed on the proceeds of a sale, only the gain.
Tom Young
