The foresight can be slid sideways in it's mounting.
If you have a No4 then the rear sight can't be modded as far as I know. If it's an SMLE then probably the same, though you could replace the sight with one that will, but that will cost you quite a bit probably.
In the end it may be easier to make it shoot straight. It may be that the inner barrel isn't lined up in the outer barrel properly.
To fix this try wrapping some electrical tape carefully around the inner barrel.
Hmmm... Well it depends on whether the part is actually real steel or not. If it's a casting that S&S has made then it could be completely different and not movable. But it's real then it should be mounted in a groove.
You won't be able to move it by hand. You'd have to use some sort of force, eg a hammer. etc... Of course you risk ruining the gun if the wrong pressure is applied.
Sorting the barrel out is a lot less dangerous option.
To check to see if could be the barrel, take a look down it. Is the inner barrel perfectly centered in the middle of the outer barrel?
Actually, the barrel looks a little off-centre in that photo, to me. It's hard to tell because of the blurryness.
The foresight has the expected groove, you can see it on the side. However I can't tell if the whole foresight assembly is original or cast. To be honest I was never sure on the S&S No4 I used to have.
The rear sight is 100% what I remember having and you have no hope of adjusting that.
Another thing that can cause the gun to shoot off centre is if the hop-up isn't aligned properly.
Glad you got it sorted. 
following up on this, it seems there is a special gadget for adjusting sights on the real Lee Enfield No4
http://www.gunshows.co.nz/documents/37.html
