Something weird here as you reported the drivers side is 1" lower but the original picture shows the passenger side lower.
I think you need to remove the metal added on the inside just so you can get a better picture of what you have. It appears that the added metal is either screwed or pop rivited in place (at least on the driver's side).
From what we can see on the driver's side pictures it appears the floor is in pretty bad shape so you may be looking at a fairly signficant task of rebiulding the cab support and floor structure. Depending on what you want to end up with there are a lot of different ways to go.
