so, in his ad, here's Vic's explanation about pre-prod serial numbering............
"Hi, Thanks. This Frame is CB750-2113, with engine CB750E-2113 It was common for Honda GP race bikes and prototypes of the 1960s to have the same numbers. The very first prototype CB750 (a few months earlier than my bike) which was shown at the 1968 Tokyo Motor Show had Frame/Engine numbers CB750-1101. The first "1" means "first series" produced of the proto, the next numbers (10) means nothing, and the last number (1) means first bike made of that first series. That bike never left Japan, and nobody has seen it since. The second series (the 4 bikes that came over together for the Las Vegas Show) were numbered........ 2110 (Gold Bike)....... 2111 -?color (Red or Dk. Green)........ 2112 -? color (Dk. Green or Red)..... 2113 (my Blue/Green Bike).......... The first number (2) means "second series" of protos, the next 2 numbers means nothing, and the last number (0,1,2,or 3) is the sequential number assigned to that color bike. (Actually, the 3rd number in each of the 2 series is a check number, but you get what I mean). Thanks again, Vic"
wonder how he knows some of the numbers "means nothing?"