Spanish 1893/M1931 7mm barrel threads question

When buying my Jap 99 rifle; I got a $50 throw in deal on a "truck gun". It turned out to be a rather well used looking Spanish M1931 in 7mm Mauser. Lots of dings and ugly marked metal. But the owner clearly kept it oiled and rust free. It is very strong and all original. But I'm guessing things may have fallen off this rifle over the years.

The front sight! A squarish post with a small hole? And forward of this post is a threaded barrel. What went here? Looks original. A barrel cap perhaps?

I see why the old fella liked it. It shoots good respectable groups. My father in law worked up some 140gr. Speer spitzer loads that settled in at 1.1-1.5 inches at 100 yards. Took a few work ups but that is fine for what I need. Which is a farm gun.

Anyway I'd like to put the barrel and sight back to original.