Beware on using the wrong stud, as there are two. One short and one long, normally supplied with Harris bipods. It is the short one that should be used for obvious reasons. Clearly a pilot hole to accept the stud must be drilled prior to any attempt to screw the stud into its central location. I would suggest a good wood/metal glue when you finally commit to screwing the stud in, as there is a great deal of pressure excerted onto the bipod when you are in the firing position.
Sorry to teach you to suck eggs, but strip the barrel away from the woodwork before drilling and use the spacer washer supplied with the stud.
Once you have the short stud embedded tightly and secured overnight with assistance from the small amount of glue around the stud thread, you will find the Harris concept, is to slacken the spring assembly and gently prise it over the stud loop and then tighten.
If you need the exact measurement for this screw location I will see if my contact still has the blueprints but in old measurement it was 2" from memory from the wood end
Good Luck
If you feel all this is beyond you, it normally is, and I would then suggest you taking the rifle to a good armourer.