After hours and hours of sanding, bleaching, etc., water damage in my sister's bathroom is irreparable. Pulled out damaged wood and am attempting to replace with matching fir from the local rebuilding center. The problem is new flooring is slightly narrower than existing flooring (100 years old). Now I'm left with about an inch gap when fitting new boards in place (the boards are 3" wide). Another problem is the wood being replaced needs to match up between existing flooring on one side, and one board on the other side that is firmly under the bathtub. Do I need to find more of the new fir and replace everything starting at the board under the tub, or is there a way to take up the gap. If I were a thousand miles away, at home, I'd just fashion a new tongue and groove board but I'm lacking tools here.

Thanks in advance for any advice,
Mark