I first welded the plates together then laid everything out on it. Once I had my layout marks set I drilled 1/2" holes at the ends of the slot locations. Then I cut them with a zip wheel on my grinder. Woke up tasting that stuff in my mouth. The gearbox I drilled 7/16th and tapped the holes for 1/2". Going into the frame I already had two 1/2" through bolts but added three more for torsional strength. The last three I tapped into the frame.