Yes, it's a later 'reinforced' bayonet. I thought these bayonets with the straight sided stronger crosspieces were from the mid to late 70's. Certainly stronger and I never saw one with a broken X-piece ring. There's quite a bit of brazing work involved in this bipod project because once the blade is cut off the X-piece will just slip off the front unless it's all brazed together! Not the sort of facility that the average crunchie would have. No good for accurate shooting with of course but like you say, across country ground level observation with the IIW or from the watchtowers, as good as anything else. Seems hard to believe that we used IIW's that size now! Mind you, they lasted for many years, right up to the L1A7 version.

What is that circular stud/nut/reinforce on the butt, just above the missing sling loop? Is it a hybrid Arctic Warfare butt with the clip-on sling loop on the other side?