Up to about a year ago I had worked for Classic Tube so while you may think I'd be biased, I no longer have a dog in that hunt. So here goes.............
The product Classic Tube builds is a quality part. Their stainless tubing flares well and normally does not require the tighten, loosen, re-tighten, multiple times to get the flares to seal. Also their tubing up to 3/8 diameter is sourced from the USA. Most tube nuts are also USA made as well as the armor guard (Spring Wrap) for their lines. If you buy the lines from Classic Tube I strongly suggest blowing the debris out of the tubes before installation. It was a step I always took on the lines I produced but not everyone working in the shop are "Car Guys". I always built products as if I would be the end user. I also produced lines for some big name chassis builders so again I built the parts as if I was the end user. If you order from NPD, G-Body parts, you will be purchasing a Classic Tube part, just an FYI. As far as fit I cannot speak on a g body brake line kit but I had installed a OE steel kit in my Dads 93 F-150 and it required no adjustment in fit. Same with a stainless F-150 kit I purchased for a family friend, dropped in with no issues. Same with a 57 Chevy Stainless kit and a 71 Chevelle stainless kit.
Don't know if this will help or not, I no longer can vouch for the quality of the parts due to seeing the change to non car guys working in the shop but they still have a level of quality the owner expects in all products not just the Mustang world he is heavily involved in.
If you purchase Classic Tube over the phone, Cliff Schultz or Tim Slattery are the salesmen to talk to.