The estate taxes were due within 9 months of death. If an estate tax return was never filed, then the statute of limitations has not started. Hopefully there is some information that you are missing here, talk with an attorney.
You will have to prove that you filed and paid inheritance taxes in order to clear title. If you cannot show a return or assessment from Dept of Revenue, the title company will likely hold the estimated taxes in escrow until a return is filed.
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If you do this the technically correct way, you will get an appraiser to give you the value in 1987 and you will calculate the tax, the penalty and the interest. There is a was to cut the corner. I often make a deal with the Dept of Revenue to pay a percent of the current sale price for a get out of jail pass. You will need a lawyer to help you.
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