Adding foreign keys in Rails 3.2

I've just inherited a blog platform that uses Rails 3.2 (!!), and I'm looking to add some functionality. I have two models, Article and Issue, which I'd like to associate such that any Issue has_many :articles and and any Article belongs_to :issue.

I've looked into using the gem foreigner to help with this, but I'm wondering if there's a way to do this without adding more gems. I've looked around SO and seen some conflicting stuff. This SO post seems to only apply to Rails 4, which I guess automatically generates this sort of migration.

Can I do this manually by migrating to create appropriate integer fields in both schemas, and then putting the has_many and belong_to statements in the models?

Thanks so much!