Well, while new engine out for warranty work, got a few pieces of o63 and o74 track to see the difference.
With the 70' passenger cars.. only 1/8" less from inner rail to edge of car. For right now, not going to change all the curves in layout. As of right now, only one area is going to be modded. Make a straight section instead of 2 almost back to back o54 curves to avoid studs.
Oh and I got a 6 pack of Menard's tankers, and one motton salt.... should have left the zip ties on trucks... when removed... they were so loose.. had to dismantle 4 of 6 car's and tighten the screws.