Have a picture of an original 603 head that shows 16... Perhaps it was a casting flash error.

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64 European Coupe Brilliant Silver with Red interior 4 Speed Sunroof
87 TDT 286k
87 SDL 195k
83 SD 202k
83 SD 201k
83 D 286k
02 R1150RT 32K
00 122HP FLSTF
07 KTM 250SX

"Danger takes many forms"