I measured both sides with the frame on and bolted from the top two bolts. Then made some marks with die punches, then measured again, etc. once I was confident I took a shot of tequila, grabbed my drill and these bits and did it over a few nights:
YUFUTOL Carbide Burr Set with 1/4''(6.35mm) Shank 8pcs Double Cut Solid Carbide Rotary Burr Set for Die Grinder Drill, Metal Wood Carving, Engraving,Polishing,Drilling https://www.amazon.com/dp/B01N1YAX4Z/ref=cm_sw_r_cp_api_glt_fabc_Q2R1QEPE0PD6JFGAT8JY