In the last clause, the original text had the modal auxiliary would, but in the 1852 LDS edition would was replaced by could (probably accidentally). The use of would actually reads better (could sounds too conditional, would is more decisive). The use of would is also consistent with the earlier use of would in this verse, “that he would grant unto us”. Here are two other examples of negotiations where a proposal involves a sequence of would ’s:
The critical text will restore the original use of would in Mormon 6:2. For more examples of textual variation between would and could, see under 3 Nephi 3:15.
Summary: Restore the original would in Mormon 6:2, with the result that Mormon’s proposal will consistently use the modal would (“that he would grant unto us … and there we would give them battle”).