For those of you who haven't changed out the resistance wire, have you checked the voltage AFTER it has run for a while? The way a resistance wire works, it will allow full 12v through when cold, but as it warms up the voltage it allows to pass will drop to its designed rating.
I personally have a Pertronix Ignitor I on my '63 with A/C and for quite some time ran Pertronix' Flamethrower coil on it in the original mounting location, which holds the coil horizontal on the side of the A/C compressor instead of vertical. I've had two Flamethrowers in conjunction with my non-modified ignition wiring, i.e. I have the resistor wire in place, both Flamethrower coils failed without warning - the first one lasted about 6,000 miles until the insides of the coil liquified and shorted itself out. The second one less than 2,000 before it crapped out on me in the middle lane of a busy Interstate highway - after sitting 45 minutes to cool down it fired off (just in time to drive it onto the flatbed car hauler I called to haul me home).
I've since put my original coil back on but haven't driven it much since changing it out. I don't know if leaving the factory resistance wire was part of the problem, but right now I'm real skittish about being far from home without both a replacement coil and either a spare Ignitor or points/condenser. I've also learned that mounting a Flamethrower coil sideways/horizontal is not a good idea because over time heat build-up will allow the windings to fall onto the case and short out. So, if installing a Flamethrower coil, mount it vertically so that the terminals are at the top.
Alan H. Tast, AIA
Technical Director/Past President,
Vintage Thunderbird Club Int'l.
Author, "Thunderbird 1955-1966" & "Thunderbird 50 Years"