Diesel
oil doesn't have as much
zinc in it as it used to; for the same reason gasoline
oil doesn't. It still has more, just not as much as it used to.
15W-40 is kinda heavy for this time of year in my corner of the galaxy. Not sure what the weather is there, but I bet it's above 25*. I don't need 40
oil in my engine because of tight tolerances. But your builder should guide you what your engine needs.
For a new engine, I use the cheapest 5W-30 dino oil I can find, and 2 bottles of comp cams break in additive (11qt system). I run that for about 30-60 minutes, and 2-3 heat cycles in the garage. Then I drain and fill with the same thing, and drain after 2-3 gentle heat cycles on the street. Then I put in the good stuff.
As for watching what's going on - good luck with that. Even at idle things are moving so fast you really don't learn much. You'll learn more by using machinists dye and rotating the engine by hand.