Last motor height question. When comparing the AV plate to the bottom of the hull, should I be comparing it to the back of the hull at the transom, or the keel that ends 1.5 feet or so ahead of it?

Assuming that you don't have a built in elevated extended transom, the motor height should be measured by lying a straight edge on the lower aft portion of the hull. i.e. The extreme rear portion of the boat that sits in the water.

Some boats have a built in extended transom of some inches. In this case, there is a space between the water and the lower side of the boat until it connects to the hull proper. In these boats, the height will be measured from the bottom of the hull, and not the bottom of the transom.

Take care
REW