1971 Dodge Demon power booster line problem???!!

So what do i get to make this work? 1973 lines?
No, like I said- you probably already have the '73 and later lines. If you do have the later disc brake conversion and proportioning valve (you still didn't say), earlier lines ('72 and earlier) may be a better fit length wise, but may not match up to your late prop. valve (although they may just need a few tweeks). The easiest route would just be to buy a roll (or a couple of short lengths) of brake line and bend your own to fit your master cylinder position, going to the prop. valve.