47-55.1 1951 3100 expanding rear section of floor pan

[hopalong]

I'm back on the resto mod of my 51 chevy 1/2 ton truck. Building back the cab floor and extending the rear floor edges "all" the way around and up to the inside of the the cap interior corners. The existing gas tank removed and new tank to be relocated under truck bed. My question is has anyone extended the cab floor at the rear corners up to the corners where there is large open area that allows outside air to come up through these openings and cover the cab floor there. I see no reason for the openings to be there except for the old gas tank needed air around it?