I am installing a new to me TM and I have been told to different things. 1- drill the 1/2 holes then counter sink them to help you not have spider web cracking, 2- dill the 1/2 holes and be done cause the counter sinking will cause spider web cracking.
I have taken the old 12/24 johnson tm off and the mounting holes are not counter sunk. But then again the johnson does not weigh as much or have the torque that the TR82 has. This is on a 1989 basshawk 181 xl.