I am looking into this two but just wonder if you have the QR20DD or QR20DE engine.
EDIT: The Both the QR20DD & the QR20DE uses the same cylinder head. This head also fits the QR25 so it proves. I am not able to find a free service manual which would be able to help with the cylinder head and gasket surfacing tolerance. You may have to end up trying Justanswer.com/nissan