From the Marlin Owner forums:
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.
