brakes went out

I purchased a 71 dart yesterday 4 hours away. First mopar, first project! Trailed it home, brakes went out coming off the ramp at home. The guy told me that it could easily make the drive home if i chose to. There is a major leak in the line. This guy topped off the fluid before i got there and it leaked on the trip home and while loading and unloading. Why can't people just be honest. I found a stainless brake line kit at year one, 220 bucks for a 4 piece front and 2 piece rear. Should I just go to autozone and do it myself? Also while im at it, was gonna replace the booster and master cylinder with a 7 inch booster and aluminum cylinder. Will i run into any problems installing this smaller cylinder?