I'm surprised.
Usually on these Factory made "kits" all of the holes are drilled so all the builder needs to do is to put things together.
Your kit seems to have been made so the builder actually has to do something more than just putting it together.
There needs to be something to hold the stock to the barrel besides the tang screw at the breech.
There are several ways of doing this but the most common is to install metal underlugs to the bottom of the barrel. Those seem to be in your last picture.
These underlugs fit into the dovetails that are milled into the bottom of your barrel. They usually need to be forced into the dovetails tight fit.
Pockets that are milled into the bottom of the barrel channel in the stock clear these underlugs when the barrel is installed.
I looked at your photos after enlarging them and it appears there are no existing cross drilled holes for the pins that will pass thru the barrels underlugs.
Hopefully I'm missing something here because if this is true, you have some work ahead of you.
More than the average newbie kit builder normally has.
You will have to assemble the two piece stock so there is no gap at the split.
You will have to install the barrel into the stock(s) after marking the locations of the underlugs on the outside of the stock.
Then remove the barrel and accurately measure the distance from the top barrel flat to the middle of the underlug. Write this measurement down.
Install the barrel so it is fitting all the way down into the barrel channel. If you have some C clamps, it is a good idea to lightly clamp the barrel in place.
Then, measuring down from the top flat on the barrel, mark the measurement you found on the side of the wood. Do this at both underlug locations.
(You must be as accurate as possible with this marking. If you are wrong the drill bit will not hit the middle of the thin flange on the underlug that is hanging off the bottom of the barrel.)
Measure the diameter of the two pins. You will need a drill bit the same size as the pins and an electric drill to drive it.
Now, you will need to drill as accurately as possible the pin holes thru the stock and thru the underlug(s).
Before you start drilling, make sure the drill is going to pass straight thru the stock, parallel with the top barrel flat.
If all goes right, your drill bit will produce a hole that passes completely thru the stock and thru the metal underlug(s).
Good luck.