Is it okay to use the cord from a Magsafe adapter with a different wattage?
If I'm reading your description correctly, then the replacement cord has a higher rating (60W) than the 45W that is drawn by the 2011 Macbook Air. This is fine because all it means is that the cord has a thicker gauge to handle a higher wattage (than what you are are actually using).

The replacement cord would not affect the voltage, so your adapter would still be delivering what it is specified for, namely the 14.5 V.