For casting, I think you'd be far better off using a zinc/aluminum alloy (Zamak) like the originals. Besides being easier to cast, many of the Zamak alloys have excellent wear characteristics whereas most common aluminum casting alloys do not. Also, if your intent is to cast a net shape gear without machining the tooth profile, the only practical way that will happen is to 3D print the gear in PLA or (or suitable casting filament) and investment cast the parts.
You could try pulling molds of originals and making waxes, then investment cast, but I think the shrink changing the pitch diameter could prove problematic. Again, a zinc alloy would exhibit less shrink.
They're still available from Clausing and used at the auction sites and various others. You can also buy blanks from Martin Gear.
The change gears themselves are not heavily stressed and can be 3D printed directly and used as is in ABS and harder printed materials. They would last quite a long time. If you can 3D print I'd just skip the casting altogether.
You have to really want to make them to justify the effort. Just depends on whether you want to make lathe parts from scratch or make parts with a lathe.
Best,
Kelly