Here is a full line catalog of Eisemann ignition products pribably from or after 1920. This can help identify products and determine which are used together to get your project up and running. The model G4 was very popular with early autos and tractors. These were used extensively by Dodge Brothers, Buick, Caterpillar, Samson, Aultman Taylor, and White trucks. They performed well and would give a hot spark even when all was not well. They suffered from the usual woes of a wound armature and icky sticky goo. Some had pot metal issues. The housings can be fragile as eggs. Beware of bad threads in the base. Helicoils are a big help. If the bosses where the internal threads are formed are cracked or broken away one can build them up again with a low temp alloy like Muggy Weld pot metal super alloy. We like it a lot as it melts at a lower temperature than most pot metal repair alloys like we see at the county fair. It works well and is less likely to cause the potmetal to explode and spatter. Once the areas are built up a helicoil can be installed.
Also of note are those typical looking threaded fasteners. They look like the usual 10-32, but they are indeed 5MMx.75 metric threads. This is not the standard 5MM metric pitch. 5MMx.75 Taps and dies are not the easiest to find but are a good investment if there are any Eisemann products on the premises. They also use a 4mmx.75 fastener in some places and on their smaller mags like the GV4.
The pot metal sleeves that form the stationary cam assembly on fixed timing/impulse coupled mags can swell, distort,crack and crumble apart on these mags. If the cam assembly ring distorts and/or swells up it can cause the cams to be asymetric and result in asymetric firing with a rough running engine. If the potmetal is reasonably sound you can bore it straight and sleeve it back to standard dimensions. If it has completely self destructed and many have, one can get a bronze bearing and bore it to size then locate and drill the holes to mount the cams. Been there done that. Sometimes shims will be found under the cams. If the point clearance is not the same on either cam, then shim the low cam out.
Some literature proposes that this fatter longer duration spark from a wound armrure design is best suited to larger spark ignited engines.
This is why some magneto distributor caps have two extra high tension connections. They start with a battery and coil using the magneto as a distributor then when(and sometimes if) the engine starts they switch the distribuitor rotor lead to magneto output.