IMHO if the action is missed you should show it with the help of perfect aspect. Taking into account that you also need to show the process to my minf the right variant will be: If I had gone to the US to study, I would have been taking the entrance exam of ABC company next year.
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OlgaaIf I had gone to the US to study, I would have been taking the entrance exam of ABC company next year.To me, the present perfect 'would have been taking', however, cannot express the future possibility, especially with the words 'next year'.
LiveinjapanIf I had gone to the US to study, I would be taking the entrance exam of ABC company next year.In my opinion, it's lovely just as it is.