Geodude -
I am in the midst of this very same thing with my '69 GTO floor - from the firewall all the way to the rear seat backrest. I purchased full-length floor pans, both LH and RH sides and a new rear seat area.
Something I saw today as new product for PY is a full complete pan. I do not recall your vehicle type, but this product may be easier than two halves. Wish it was avialable prior to my purchase.
Perhaps something to consider if available for your vehicle and you have not made the purchase of two halves yet.
1969 Restoration