The C stands for carbine. Here is a list I've found concerning the rest of the letters:
CS .... Carbine Safety
C........ Carbine. 1968 and up
RC......Regular Carbine same as C prior to 1968
T .......Texan. Carbine with straight stock, 20 inch barrel
TS.......Texan Safety with 18.5 inch barrel.
SC.......Sporting Carbine, 20 inch barrel, 2/3 mag tube, pistol grip.
CB.......Cowboy, 24 inch octagon barrel and straight stock.
A.........Prior to 1980 24 inch round barrel PG stock
A........ Most recent, 20 inch PG carbine with birch wood, end cap forend.
W........ 20 inch PG carbine, birch wood, and two barrel bands
Y......... Spikehorn youth model short PG walnut stock 16.5 inch barrel.
LTS...... Texan Safety, 16.25 inch barrel.
Marauder.. same as 336 T except has 16.25" barrel and SG. Roll marked RC.
ER......... Extra Range PG stock in 356 Winchester.
375....... PG stock 20 inch barrel in 375 Win.
XLR.......Stainless steel 24 inch barrel PG laminated stock
CC....... 20 inch carbine with camo pattern birch PG stock
SS........20 inch PG stock Stainless steel.
ZG....... Zane Grey Century PG stock, 22 inch octagon barrel.
336 Octagon.. 22 inch octagon barrel SG stock.
336BL.... big loop lever and laminated PG stock.
Do you mean the Remington model 700 bolt action rifle?Marlin never made a model 700 to the best of my knowledge.
RC=Regular Carbine
Regular Carbine.
Glenfields are Marlins marked for sale by 'second-tier' retailers.
This may- I mean MAY be your rifle. It's a model Marlin Model 49 slide action Shotgun. Exposed hammer takedown combined features of the model 42 and 24. It was never in the Marlin Catalogue. It was made between 1925 - 1928.
10Your glenfield marlin 30-30 model 30 was made in 1966 according to marlin arms chart.
Do you mean ejecting?
The letter J was used by Marlin to indicate what year a rifle was produced.This system was used from 1948-1968.The letter J indicates that your Marlin model 336 SC(sporting carbine) was made in the year 1952.I hope that you find this informative.
This means established 1820.
The RC stands for Regular Carbine, the R was later dropped and just 336C used to describe the Carbine style. The style refers to the barrel bands that also go around the forearm.
The letter G prefix to your serial number indicates that your Marlin rifle was made in the year 1950.
Long and Long Rifle.