That last photo tells the tale. If you look closely, you will see that the markings have been applied in two different batches.
First batch tells you that it is a Government rifle (Crown and Royal Signet GR representing King George V). BSA Co. tells you that it was a contract-made rifle produced by the Birmingham Small Arms Company in their Small Heath plant at Birmingham. 1915 is the date of original manufacture.
Now we come to the fun part. The original marking, which has not been scrubbed entirely, read "Sht. MLE" on one line, with a Roman "III" under it. This means that the rifle was a Short, Magazine Lee-Enfield rifle, Mark III: a .303. This marking would have been scrubbed when the rifle was altered to a different model, in this case to a Mark IV*, which happened to be a .22" rimfire rifle.
Don't get anyone wrong here: the .22" rifles were not toys for boys; they were valuable instruments for teaching the elements iof marksmanship to recruits, for use on restricted indoor ranges, and for diagnostic shooting as well as for teaching how to correct shooting problems. An added advantage was that a .303 round was loud, recoiled hard and cost 7 cents, whereas a .22" rimfire recoiled but little, made little deafening noise and cost half a cent.
The barrels on military conversions WERE tubed (lined) but the people doing the work were experts at what they were doing AND the steel they used in their liners was the same type as used in the original barrels, so it browned (blued) the same colour.
That Ross rear sight was used almost exclusively on Canadian target rifles. The special rear-sight mount was made by Howard W. Cooey in Toronto. He also made many Ross Mark III rear sights on contract, so this also could be his work: look for a little HWC in an oval. Also look for a C with a Broad Arrow ( like this: /!\ ) inside it. That is the Canadian Government ownership mark of the period.
The Ross, once restored properly, will be worth the guts out of a grand, the Lee-Enfield about half of that. You are having a couple of Very Nice Treasures dumped on you. If I were you, I would take the man shopping and get him pretty much whatever bow he wanted. That way, he will be set up the way he wants to be.
YOU, on the other hand, will be set up for THIS YEAR: 2014 is the 100th anniversary of the outbreak of the Great War for which both of these fine old rifles were made.
Go buy a lottery ticket; you're on a roll!