Whats are those marks on my mosin?

Hello to everyone who is reading this discussion.

First I want to say that english isnt my language, so I apologise for some posible mistakes...

Now, after reading some text and seeing some pictures on this site, Iam little confused about some marks on my mosin.

I have 3 questions in general:

1) What is that "crossed sqaure" mark on stock?

2) When this rifle is from 1926 (as you can see). So if I know well, before 1930 was Izevsk mark "arrow with bow" and after 1930 there was "arrow in triangle".

So, why I have that later mark under rear sights? (rifle is numberd comletly).

3) And last one, whats that "H" letter on stock? Is it replaced stock?

I bought it from Belarus reservs. And it looks like it never seen action. It was covered in vaseline.

Thanks for answers :)

Greetings from Czech Republic