The answer to the question above would be that the sentence that provides the best version using subordination is the following one: While I would be able to attend the party, I could only arrive after the meal. That is, the correct option would be D.
In the original sentence, "only" empasizes the fact that the speaker will be able to attend the party after the meal. In the new version, the conjunction "while" has been introduced to show the contrast between the two ideas.