Is this short year the first tax year of the estate? If so, the estate gets the full $600 exemption.
If this final estate tax year is not the first tax year of the estate, I don't think that you can change the end date of the estate's tax year (at least not without requesting and receiving approval for the change, Form 1128, and I'm not sure that that's possible). In this case the final estate income tax return would not be for a short tax year and the estate would again get the full $600 exemption.