1916 Lithgow SMLE Mk. III

[Homer]

Not two serial numbers, one is the inventory number for the military district it was issued. That is the number that is also stamped into the butt.....although, I'd question the origins of that stamp, it looks more recent to me. I could be wrong of course.
Yes, forends were modified to suit the larger diameter of a heavy barrel.
And yes, this rifle would have been manufactured with volley sights, but this forend is not the original to this rifle. Again, it looks to be very early English. Highly likely the original forend would have been Queensland maple.