<VV> spark plugs

[rhmc at bellsouth.net]

Pulled the plugs out of my 62 Spyder today  #5 and #6  (the most difficult to remove), have been resized to 18mm by a PO. One side has an AC 45 and the other side has an AC 45ff. the 45 is tapered above the threads the 45ff has a flat surface with a gasket. the hole that has the tapered plug has a flat surface. 
  Can someone tell me what a compatible 18mm plug would be? I replaced the other 4 with Bosch 7902
    Thanks for your help
Bob