Repower of 1970 era 24' Skipjack

Purchased Doghouse 's old Sea Ray. Thanks again Jeff for the help and price of the total package. My son went back to Vegas to try to find work so I am alone doing this project. John is rebuilding the outdrive, got some burnt bearings, but when it gets finished it will be completely rebuilt and should give me many years of good service. To the point: I will soon begin to remove the engines on both boats. My question is, does anyone have much experience on setting the template and a aluminum plate on the Skipjack transom? I will probably have to fiberglass in the OMC hole, on the Skipjack first. I will end up with a 3/8 aluminum plate sticking outside edge of the Volvo transom plate, about 2.5 inches. John will be my resource, so I should be in good shape. I need to make all preparations before he shows up. Just looking for some does and don'ts. Thaks Al