The cam sprocket is generic, #1 dowel hole and outer chain alignment mark are for the L16, #2 dowel hole and outer mark are for the L20b, and I heard #3 dowel hole and outer chain alignment mark are for the Z car, this is what I heard what #3 was for.
These alignment marks only align properly every 12/15?? revolutions of the crank, so how they aligned on #1 mark in your video might be luck/a fluke, is the dowel pin in #1 also?
I have never owned a Z car or any of the engines that came in them.
Also I got distracted and didn't see all the video, but you tack weld sheet metal otherwise it warps, this is how I weld sheet metal when I make a kingcab, it has never cracked the bondo after covered and painted so far.