My motor is currently being rebuilt do to some major issues cause by the last person who built it for my grandfather before i inherited the car. During this time im trying to find out a little more about this motor and learn its history. Serial number is MN426293851869 So far i have its Marysville Plant, 426 cu.in, August 13,1969. Here is where im lost. # 51869 after the date code is that the serial number? Any what the 2 and F stampings above?