Ethernet to SPI converter Differential line importance?
At 10 Mbps (which is, if I recall correctly, the only line rate that those chips support) you don't even have to bother with getting the impedance right due to the length of the traces. Just route it differentially and don't bother with the length matching.  And don't add resistors, that's not how you fix a bad impedance match - for that you need either a re-spin with fixed dimensions or a matching network.