Looks like valve stem orings. You shouldn't here one cyl clatter above the rest. If you are using actual 6.2 long body injectors,they won't work very well. Especially combined with diamond precups ,which are very unforgiving to wrong timing and or coarse spray patterns .
Could be a clogged lifter,or broken valve spring. A bent valve is not likely. If you got too carried away with valve lapping,lifter preload can be excesive.
Yes, it has a pinch bolt holding it to the throttle shaft. This will adjust idle and part throttle advance. There is also adjustment at the bottom of the arm,got to be careful with that one , it changes timing everywhere.
Your head and rotor are worn. Thin fuel will just leak through at cranking speed. I had to lower my pop psi from 3800 psi down to 2000 psi so it would start hot. To run high pop psi injectors you must have a very good head and rotor. Or run waste oil with a worn pump.
Iv'e tried it,didn't work and fried the heat gun from leaving it on way to long. Was one of my motors with a very low compression ratio,and a cam with overlap. Put new glow plugs in and it started fine.