I probably wouldn't bother. The coaster brake works okay for what the bike was intended for. And if you're riding fast or going down mountains, you probably don't want to be using an old fork with holes drilled in it, anyway.
I don't know how much the wheels differ. But the bikes with rod brakes have a different rim (I think) from normal bikes, and the older steel rims may vary as well. Check the rim geometry and see how it looks.
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