After considering this a bit more, I'm leaning towards the idea that this type carb (E4M) might be a better candidate for modifying it to be used w/o primary needles, and run off just jets (dropping the size by 5-7, like the book mentions).
Prolly just not too practical to try to convert it to non-ECM (M4M) use- cores are still readily available to make it a viable alternative.