Frontier is now Hornady. It was the original company started by Joyce Hornady to reload spent military brass with Hornady bullets. They had to start making their own brass when the Vietnam war came about.
http://www.hornady.com/about-us/history
As far as the brass you have, I don't know but I would guess that it should be fine since it's been indoors this whole time. I agree that it's going to take a lot of work to get it back to the correct length and size.
HTH!