A500/42RH Trans Fluid Level

Lets say for reasons I can't remember, I had to modify the tube and dipstick for the 42RH install into a 68 Dart and use the truck dipstick with a A904 tube. I want to cut and engrave new markings on the new dipstick. What is the correct fluid level (running & with pump running) in relation to any point of reference? I could use the case to pan line, the bottom of the dipstick hole, some point on the valve body, really anything as a point of reference. I have a deeper pan and filter extension block, so relationship to filter won't work.