Angle, good point. Thats why I asked first. Measure twice cut once.
FWIW: I installed the new transom before drilling any of the holes. Many/most were on some angle. I used a smaller diameter drill to go half way thru (about 3/4"). then came from the outside to meet in the middle. Then used the right size from the outside. The drill will follow the hole. Filled holes with 5200, from caulking gun, from transom side, and pushed the bolts thru. Cleaned off the threads, and added washers and nuts,