The curvature of the race area doesn't matter, as long as the small and large diameters span the actual track width (they all will). The balls are smart and find the right diameter tracks in the cup and cone, because that's where the gap will be widest as you bring the cine into the cup. Kind of like making snowballs.
The length fo the cone matters a bit because it can affect the axle width, but most are close enough. So all that does really matter is the thread (duh!) and the OD, since that affects the gap in the seal, which is important if you ride in wet or dusty conditions. Most common cones are pretty similar, but you might measure th OD of the old cone and ask that of the replacement candidate.
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