Final answer:
Old Grannis is involved in preparing the wedding as the best man, reflecting on the nobility of marriage and what Miss Baker might think of the ceremony.
Step-by-step explanation:
In Act 4, it is Old Grannis who is delighted beyond measure at the prospect of acting the part of best man in the wedding ceremony. He engages in preparations with a reflective mood concerning the institution of marriage. With details scattered across the given references, it's apparent that multiple characters are involved in wedding preparations. However, Old Grannis stands out for his role and his anticipation of what Miss Baker might think of the event, indicating his personal investment in the proceedings.