Floor repair correction?

[Dakcrew]

I am going to start my floor repair shortly and have been looking at the cab and noticed that I have the usual rust in the rockers and a bit in the cab corners, but what concerns me is a gap between the floor and the firewall. I have been looking at it and there seems to be about a 1/4 " gap over the hump between the floor pan and the firewall that was there from the factory. half of it (passenger side) has a huge glob of seam sealer filling the gap, but the driver side is empty.

The question here is should I just fill the driver side with sealer (assuming there is no unseen rust...) or try to pull the pieces together, or fill with new metal?

Any help would be greatly appreciated. Thanks.