I think you are going to have to trace your wiring back to find the HV line as the wiring diagram shows. Other info you put there does not really help.

SCR may have different characteristics so you would have to check there.

Cap used in other systems are 470nF/400V (474k)rather than the 68nF it shows in the diagram or the 1000nf you have there. There may not be enough time to fully charge the one you have used but something should work.

I imagine it would not hurt to try 470nF though.

Diode you refer to would probably be a schottky diode (fast) and not standard diode as you have used.