Property valuation for capital gain

Did you wrote an application to the sub-registrar requesting the transaction amount at which similar properties in that area were sold during 1981 ? If not then kindly do the same

They will provide you details of several transactions from which you will have to compute WEIGHTED AVERAGE value per unit (eg Sq yard)

Valuation with 10 years variance should not be accepted.

Alternatively you can request the AO to refer your case to the Departments valuation officer and they can find the value for you.