I opted to put the holes right where the prints called for them to be, in the end of the tanks. I figure with a little sealant it oughtta work just fine.
Made the holes 58.5mm then opened them up while deburring and polishing edges. When the flange just fit in the hole, deburring stopped and polishing began. Hole size is 58.92 (2.320) The inner piece just fits in and the five bolts fit inside the hole.
