Ignore Sunray, he has a fixation on headspace.
Head space or bore diameter will have no effect on the setting of the bolt bearings.

Bolt bearings can be done on a stripped receiver without a barrel.

Continue. You are on the right track.
First step is to get an even bearing on both bolt lugs, THEN check your headspace.

Use candle soot as Green suggests, or a kerosene lamp flame works well too.

Your bolt head has seen a LOT of rounds. The primer erosion on the face just looks like crap but will still work, but maybe time to change it out.
Most cartridges sit a little off center in most large mil spec chambered rifles, it is a LE quirk that can freak new LE owners out. It wrecks the brass, which was designed to be a one shot use and disposable. Nothing to be concerned about unless you reload, then there are work around solutions if it does become a reloading issue.
But who can say if this bolt head is original and that the erosion was from use in this rifle? The pudding test is to check a fired case.

Trigger guard should tighten down and bear on the bottom face of the trigger guard inletting. The amount of crush is set by the front trigger guard screw bushing. It is important to the correct breeching up of the wood to action. Trigger guard set up has a MAJOR effect of how the rifle shoots.

Poke around to find postings by Peter Laidlericon. He has done this a few times and has written some excellent instructions in layman's terms.
Everything that you need to know is right here if you do a search.