Well as far as dating a Marlin I found this...
"The first two digits of the serial number designate the year of manufacture, either as the last two digits of the year (in 1969-71) or as a number code (1971 and later).."
http://armscollectors.com/sn/marlinlookup.php
There is some other information for rifles of different time periods. Time to go home and look at mine. (I really need internet at my house.)
Thanks perpster. I will keep that in mind.