Without knowing how the engine is mounted on the transom, the weight of the boat and load, all anyone can do is give a guess based on their experience. Since you never mentioned what prop was used on the old boat, or what rpm it attained it is not really relevant
If I were rigging it with the engine at the lowest transom height, I would start with a 17 in pitch and see where the rpms are. Your engine has a WOT rpm range of 4500 - 5500. That engine does perform best when propped around 5300 - 5500 rpm