Jesse,
I purchased a complete gasket set on eBay.
Once I completed the teardown, I made a list of the parts I needed to go back to stock. (I looked into acquiring a J15 motor from a Datsun Forklift, however all the J15s I found were considered "rebuidable", with no warranty attached.) Since I had to do a rebuild, I decided to stay as original as possible.
Be advised, because no one vendor (or Nissan dealer) has all the parts for a rebuild, UPS charges added to the cost of the parts.
Keith