cylinder/ what year?

I have a pair of twin cam cylinders and I am trying to figure what year they are. There is a plate on the top of the unit that has the following number (16593-99). The number 3 looks like it was stamped at a different time or in a different way and is a little larger than the other numbers in the string. This leaves me to suspect that it may be an 03 due to that, but that is just a guess. Does anyone know if that number is telling me the year. The local Harley parts counter put the number in his computer but it told him nothing. I just need to make sure that it is not an 06 pair. I need jugs that are 2005 or below. Any help would be appreciated here.