Ok, from the pics the receiver looks to be all original and in pretty good nic. The charger guide, (both the fixed part on the left wall of the receiver and the sliding guide on the bolthead) are correct exactly as they are. Only obvious non original bit on the receiver is the safety lever- it's a MkIII. Even the Sparkbrook volley sight post may have been orig.
If the bolt has a number struck out with three lines then re-numbered with serial matching the receiver, best bet is it was replaced from 2nd hand bits in service.
By the look of the rear sight set up, I'd say the barrel has been replaced, (MkIII). The foreend is definately MkI in the back (although it looks to have been converted by bubba to take the rear sight ears) and MkIII in the front half. The front handguard is MkIII but the rear handguard is MkI (and combined with the bolthead would probably be worth more than what you paid for the rifle).
Personal opinion, I think the rifle has been someones restoration project. It would be worth what you paid just to have it sitting around on the chance the correct foreend comes up. Then with a nosecap, which I believe are still available in the US, and a bit of fiddling with the front handguard, you would have a near enough to complete example.
Force matched wasn't a term used in the Commonwealth system. There were levels of repair depending on the severity of the fault with the weapon. Starting with Unit Level Repair, then it was Force Level (both of these levels are within the deployment). Next up the scale it was sent to Base Workshop or further to Factory Repair (or even FTR) Once a weapon was inspected by an armourer, he would decide what it needed, and that would dictate how far up it went. Depending on the support they were getting, force level could have been changing barrels and fitting different bolts. Whether they were engraved or stamped would depend on the repair level's authorisation and equipment to do the marking and the specific instructions for carrying out the work.
Here's two pics I just took to demonstrate the charger in the two piece charger guide set up. Once the bolt is withdrawn to the rear, the sliding charger guide on the bolthead is stopped by the lug on the right rear receiver wall. This aligns it with the left fixed lug and allows the insertion of a charger. Fist pic, charger fitted, second close up of lugs on the charger and coresponding slots in the guides
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