PY member Bruce Meyer pointed out how deep the '59 pan looked compared to later pans, in the Street forum where I'm running this same thread subject. I really hadn't noticed it myself, but I was curious and got out the tape measure.
Good eye on the oil pan Bruce.
I measured my '64 421 HO oil pan and it is
6-7/8" deep at the center of the flat portion of the sump to the top of the pan rail.
The 1959 pan measures
7-7/8" in the same spot, one full inch deeper.