The foam is a very poor substitute for tar. The tar is to hold the solder joints and everything else from vibration. I have repaired many with either nothing or foam added when rebuilt and come to me with solder joints just broken with vibration and never one returned that was completely full of tar...with nothing left to vibrate.
The smaller, 630V capacitors at 8:11 appear to be the incorrect type (Metalized Polyester Film type; eg. Panasonic Type ECQE(F)) with low dV/dt rating; if so, they will likely fail with use in the Model T ignition coil application. The larger, lower voltage; 400V capacitor at 8:25 appears to be the correct type with dV/dt rating >600V/us which is required for the ignition coil application. The next important step is point adjustment for equal and consistent firing time. For that, there is no better tool than the ECCT. It is the only coil tester that actually measures dwell time to fire spark. More information here: www.modeltecct.com
Please reconsider your use of expanding foam to replace the tar. 1. The expanding foam is an insulation . So the box may feel 'cooler' because the foam isn't conducting heat to the exterior as well. 2. I would be shocked if the dielectric strength of the polyurethane foam is anywhere near that of the tar. 3. Having worked in a factory that builds radio units for utility companies, the potting compound used now is still has properties remarkably similar to tar. Even though it is epoxy based and far better spec's overall the tar is still a better choice for the coil box than polyurethane foam I suspect. Good video. 👍
