Floor not level? Rusted

[GMC1965]

My cab supports are pretty rusted and the bolts in the floor are no longer there. I will replace the front supports and fix floors. The problem is the cab floor seems to not be level. They slant from the middle to the doors. Is this the right way or are my floors bent? I am going to be removing cab and it seems that I need to weld in support bars so the cab does not move. with floors not straight is this a problem? Doors are pretty good closing and opening. Just the hinges need rebuilding, I have the parts.