Trying to know more of this mk3 ishapore

[krinko]

Well, I'll give it a shot...
You have a lot of questions and I have only a few answers---so let's dispose of some of the unanswerable questions first.
1.Many of the mysterious small marks that bother you were applied at the factory during manufacture. They meant something then to the people building the rifle, but these meanings are lost.
2.There are small inspector's marks from Ishapore on your rifle in various places---(R)FI and (I)SA over numbers are Ishapore marks. The "EFD" on the trigger bow is an Enfield Lock inspector's mark. The "N63" on the back sight is for "T.Senior, Atlas Works, Liversidge, Yorks" which means this sight leaf was made during WW2.
3.The barrel, 81006 D, was most likely assembled to this receiver after it had already been on the original 81006 D receiver. I say this because this receiver has been numbered to the barrel with a slightly different set of stamps and the "D" suffix has been omitted. This receiver's original serial number would have been removed for this operation. The mark after the square is ["] meaning "inch", as in "pounds per square inch". The "R" on the left side isn't a "rust" mark, it's probably "replacement".
4.The bolt is not original to the rifle. The large grind mark on the rear of the bolt handle indicates the removal of an earlier number and it is not procedure to mark only part of the serial number (006) in that location. So it isn't an official replacement bolt.
5.The forestock is a post war Ishapore type and this, combined with the other mixed parts---like the nosecap---would seem to indicate a rebuilt sporter, or a rebuilt parts gun. And I do not mean rebuilt at a government facility---sorry if this is bad news.
The single most interesting bit has got to be the "N 63" marked sight leaf---at least to me, since WW2 Enfields are the only ones still in my possession and I have never seen that mark before.
At any rate, you should be able to shoot this one. If you are worried about headspace and safety because of the unofficially replaced bolt, tie it to a bench and pull the trigger with a long string. If the bolt doesn't blow out of the rifle and go screaming past your ear, you can move up to holding it in your hands.
-----krinko