Ok here is my method of drilling mount holes for engines. Learned this from my mentor who is.........precise....about how he does things. Its slow, but its the most accurate method Ive ever tried. Fit the engine to the mount. Mark one hole location, only one. Drill this one hole. Refit the engine and secure that one bolt. With it secured mark another hole location. Remove the motor, then drill this second hole. Remount the motor and secure now with two bolts. Mark hole 3. Remove motor, drill hole, and repeat the above process until all 4 are drilled. Its slow, its tedious, but there is nothing more accurate for drilling out engine mount holes.