Impossible to answer without a descriptio of ALL markings and who made it.
No, a Marlin 881 stock cannot fit in a model 81. The stock would fit an 881, not an 81.
model 881
33% of 881= 33% * 881= 0.33 * 881= 290.73
881 = DCCCLXXXI
It is 881, itself.
881 is a prime number. Its only positive integer factors are 1 and 881.
Roughly 150-200 if like new around 110-150 if showing some amount of wear.
881 x 1
881 is the 152nd prime number.
As a Roman numeral the equivalent of 881 is DCCCLXXXI
881/2500 3524/10000
881 kg is 1,942.27 pounds.