cab corner to floor gap help

[saon]

changing the rear outer floor panel, under the gas tank and the cab corner on a 72 c-20.
When I place the floor where it needs to be and line up the cab corner with the rocker, door, and rear cab panel, there is a 2 inch gap on the lower corner behind the door pillar where the floor should reach all the way to the outside cab corner.
Am I missing another patch piece?
Both sides are rusted away so im not sure what is suppose to fill the gap?
I guess I can make a piece to fill it but something seems to be missing.
Any one have a pictures of that area? or a link to some?
Thanks