Ok. All of the individual major parts (rifle, scope, & bracket) are genuine. The rifle looks pretty honest to me. Frankly I wouldn't have given the mis-matched mag a second thought. I'd just fit an un-numbered brand new replacement. As JM pointed out it looks like the bracket is mated to the rifle, suggesting that at some point the original Mk3 scope has gone missing. The 1943 dated Mk1 is clearly a replacement. The damaged grat is not a big issue if you blow in the right ears on this forum.
The low (two digit) numbers on the cradle caps are perfectly ok. They started numbering them at 1,2 then 2,3 then, 3,4 etc. Consequently three digit numbers are ten times more common that two digit numbers, which in turn are ten times more common than single digit numbers. But they all exist. I used to have a bracket with the cradle caps marked '6' & '7'. Never found a '1' & '2' yet, but I'm still looking!!
Yes, the serial of the original scope to this rifle is a Mk3, but 1944 rifles are strange beasts in that they can conceivably be found with Mk1, Mk2, Mk2/1, or Mk3 scopes! Most will be found with Mk2, 2/1 or 3's, but William Watson were very late changing over from Mk1 to Mk2 scope production as the factory was bombed, & they were still producing the Mk1 scope into 1944. I've owned three 44 dated Mk1 Watsons over the years, & still have one of them. The few I have seen have all been in the 14,000 serial range.
Sorry, I'm starting to ramble.........!
ATB.