Just figure on replacing both...then you don't have to worry about it. I believe that if you drop the center link you can replace them both with the engine in the car.
Pan gasket will show seepage down the sides and/or front of the oil pan (separate gasket for joint at timing cover); rear main will show contamination of clutch or oily (not trans fluid) torque converter and ring gear.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching