I bought an old pump 22 two days ago at a pawn shop for $195.
The upper is from 1909 and the lower from 1910.

I did a search and I see some evidence this is normal
http://homesteadparts.com/shopcart/pid_1736.htm

I have several 06s and haven't seen screws like that..I'll have to take a look..

This one was in a pawn shop of ~ 1,000 guns.
I asked to look at the guns that were not good enough to display.
This pump was in that pile May 13, 2016, my lucky day:)

It has a broken screw, a missing screw, and a new Win factory replacement barrel installed by Bubba with a pipe wrench. That barrel, unlike the rest of the rifle, is conspicuously blue, scratch free [except for deep pipe wrench scars], and has newer Winchester symbols.

The missing screw on top is 3-56 that captures the firing pin. Without it, the firing pin can go to far back and the action does not close on the forward stroke. I can shoot it if I am mindful of that, but new screws are on the way from Homestead.