An older Sun machine that shows all eight ignition traces at once on one screen would be valuable to insure there is no crossfire happening.

These single wire readout devices that give: peak KV, burn time in milliseconds, and burn KV

https://www.ebay.com/itm/Kal-Equip-Spark-Analyzer-2969-/202107367670?hash=item2f0e89b0f6

Have helped me.

I now have two I bought used so I can compare two cylinders at the same time,
or compare one cylinder to the averages of all eight by clipping to the coil output wire.