I'll try one of the e-cores transformers also... the reason I use the ferrite toroids is because they are very small and light. I also ordered the ferrite toroid cores from the same company. I have many types here and all work about the same for me. The e-core you mentioned in an old computer power supply..where is it? inside the power supply cage or on the mother board? I've taken alot of the toroids off the mother boards and all of those have been working great for me. Most of those were light blue in color..not sure of the mix for the cores. I only had one that didn't work and the secondary windings got shorted to the core because of a knot in the wire somewhere. I cut off all the wire and started over and it's in use now as a test board in my plane.
I'd like to make a combo board with cdi & timer in a square configuration.. started to make one and lost interest for some reason. I need an aluminum box of some sort to encase the boards together when finished for RFI protection. I have an old CH unit with cdi board and a modelectric coil inside that I just repaired and that works great..The scr went bad so I replaced it with an EC103d .8 amp and it's 100% functional.. Wish I had some of the Synchro-Spark timers..they worked well for me for many years. This is whay I got into making the timers in the first place..making replacements.

John