Future in the past tense

Hi Teachers,

Just a year, and I'll be free.

The above is future in the present tense. If I want to narrate this in the past:

Just a year, and I would be free.

Can 'would' be used in place of 'will'? Or must we write 'Just a year, and I was going to be free'

Is there a difference between 'was going to' and 'would' when used in this future-in-the-past context? Or are they interchangeable? If not, how to know when to use which? I am only talking of using "WOULD" in future in the past here, NOT subjunctive, conditional etc.

Thanks.