Brake line question

[RBR]

I'm getting ready to get my wilwoods front and rear going. I have a new sub frame and kept my old brake lines from the stock drum front and back. My question is can the old hard line be reused from the master back to the rear end or should I put all new lines in? I kept the old line covered on both ends to keep it clean. Can I flush the old line out with something to insure it is clear of any contaminants? This is going into a 69 bird with a new moser rearend and subframe.