Tell the Toyota dealer man to start using his head. Normaly he always wants the VIN number, types that in the computer and can then get the correct part for any bit of the car. Remind him that the computer only goes back to about 1985, and before that they didn't use a full VIN anyway, just a model code and serial number. Telling him "Celica GT" from 1972 to 1982 will sound vauge, but 18R-G / 18R-GEU engine should be enough info. He will have to look it up in a book, the part may be ex-Japan and expencive.
Best get a gasket set from Burson or Repco which is much easier and cheaper. Even better, do what I do and just use seal packing (silicon).