Use of "fueron"

Question

In the last sentence "Fueron unos días muy felices."

Isn't "fueron" the third person plural (preterite) of "ir"? It should be followed by "a"

It seems to me that it should be "fueran" instead of "fueron"

Answer

The verb in this sentence is Ser not Ir. They are exactly the same in the preterite.

Answer

Hola Joe
I am not quite sure why you want "fueran" instead of "fueron" Do you mean that we need the verb in a feminine form? Verbs don't have gender. 
The conjugation of ser/ir in El indefinido is this:
Yo fui, tú fuiste, él/ella/usted fue, nosotros/nosotras fuimos, vosotros/vosotras fuisteis, ellos/ellas/ustedes fueron
Inma