Currently readJSONheadedASCII always returns an array of type object, even if a converter has been specified. It converts element-by-element. Ideally it should return e.g. a float array (not just an array of float objects) for floats. I poked at the idea of trying to apply the converter to the whole array first (and use the current code in the except). There's not really a simple conversion function to change the type of a numpy array, so you'd have to pass in something like "lambda x: x.astype(numpy.float)" as the converter, and at that point it can be easily done outside.
This would be a fantastic thing to have, but I can't figure a good way to do it.