My guess is that it is the serial number. The model 56 was the first of the Marlin "Levermatic" line of guns that featured a clip magazine and a very short throw lever that allowed the shooter to cycle rounds through the gun more quickly than a standard lever action rifle. From it came the Model 57 and 57M which were tubular magazines of the same gun and the model 62 which were .256 win. mag and .30 carbine versions of the "Levermatic".
I believe you have a Marlin 35 Cal. Model 336 CS rather than a C5. Look again.
Marlin 81
Made by Marlin....same as the Marlin Model 80
Made by Marlin....same as the Marlin Model 80
model GA22 ( great american 22 cal) first production 1983 same as marlin model 75C
your marlin model 336sc(sport carbine) was made in 1951.
A Marlin model 30AS is a leaver action 30 cal hunting rifle starting production about 1985
Marlin model 80
No.
Made by Marlin
about $125 to $ 325
I can say that the Marlin model 81DL was made from 1940-1965.This was a promotional model,made by Marlin.