I haven’t concluded anything yet. I try to base any conclusions on as much evidence as possible without relying on assumptions if possible. But my educated guess so far is that the tape is around 1-1/2” to 2”. If you could inform us about whether or not the slot in the wood fore-stock is over-cut or not, that would be more information we could use to try to better form a conclusion regarding the sizes that you are asking about.
If you could inform us about whether or not the slot in the wood fore-stock is over-cutI don't understand what you mean by " over cut"...... I have several carcano's and one rough stock that was manufactured for the model 91/38 short rifle but it never was assembled into a complete rifle. it is cut and drilled and ready to accept the metal pieces to make up a complete rifle.
The bayonet slot is cut into the wooden foregrip. It is 3/16 of an inch wide by 3/8" deep.....it extends 3 1/2 inches to the rear of the front end of the foregrip, The sides of the slot are parallel over nearly the entire length of the slot......but they gradually narrow to a width of 1/8 inch at the rear of the slot about 1/2 inch from the rear or end of the slot. At about the same place the slot starts to narrow the 1/2 inch depth of the slot starts to decrease . ( Probably matching the tip of the bayonet blade that it was designed to accept )....
I hope this answers your question......