Used between 1973 and 1978 the Body Prefix of O18xOBnMnn can help tell you a few things about your Moke as it left the factory.
The breakdown for the O18 series of Mokes goes something like this.
O18 - the 18 comes from drawing/design office number for the Moke starting back in 1964, YDO18. The first character is an Oh not a Zero.
C or F - The C was used in the first few years and replaced by an F in the 4th position to represent the ADR specifications at the time.
OB - Buckboard body style. A hang over from the original prototype.
n - The trim level, 1 being for the majority of Mokes, while the early Californians with all the options had a 2.
M - Manual Transmission.
nn - Engine size. 09 = 998, 10 =1098 and 12 =1275
The change in the body prefix system at the start of 1973 saw the last few months of the Export Mokes, up until March 1973, have the Body the prefix O30COB1M12 to match the drawing office designation of YDO30.
Serial numbers started at 5001 for the O18's while the O30 Mokes continued from the last serial number used in the YJBAB range for the Export Mokes.