Pan rail gaskets thin???

I am currently prepping an engine for my 63 F100.  At this point the pan is just a dust cover.  The bolts are installed to the softest setting possible on a cordless drill.  I have not tightened the pan down hard because I will need to remove the pan, and I wanted to compress the gasket only once at final assembly.

The gasket is one piece rubber with grommets.  Note the pic.  The joint at the top of the pan seal is a very small amount larger than the sides of the seal.  Note that I have cork rail seals in addition to the rubber gasket, because it doesn't seem that there would be sufficient clamping on the rails.  Rather, I would deform the pan rails because the end seals would be down tight before the pan rails were tight.

This is a Milodon pan.  I had a stock Ford rear sump pan before this.  It seemed to fit the same.

The data entry area for this message says "Max size per file: 0Mb". So I put the pic at the bottom of this album.
https://photos.app.goo.gl/ECEiFoJbRKBVPSnJ7

I have used the ford one piece 460 oil pan gasket a few times. Have to use uni bit to enlarge couple of bolt holes. Sealed up nicely

If the oil pan has scalloped side flanges, (not merely flat), the one piece gasket seal will leak because the surface deformities won't match  each other.
An oil pan with scalloped side rails NEEDS to use a FLAT rail gasket,

In either case ... I find or make some load spreaders, (as is used in O.E.M. with the one piece gasket seal).