Original 66 brake lines: do I need to replace?

[sstpeach]

So this question has been bothering me and I have not seen discussed. My 66 has the original brake lines and upon inspection appear good. No wear and tear, rub marks etc.....they look good.

Currently I'm replacing wheel cylinders and master cylinder while I'm doing my brake line. I'm splitting the one line from the front crossmember to a dual line to the new dual drum impala master cylinder. (I read a post on this earlier this week)

So without any obvious indication of wear to the brake lines, and hopefully within the next few days I will find out if the truck has any issue of building up pedal pressure I have to assume the brake lines are good and should be safe for operation. This truck has not been on the road for over five years...... Input please......