How to replace brake lines on 1976 Rabbit?

I have a 1976 Rabbit.

I have been having a problem with my brake pedal slowing going to the floor
when I held it down. I did not see brake fluid leaking anywhere, so I
replaced my master cylinder and installed new pads and front brake hoses.

But, we went through two big bottles of brake fluid trying to bleed the
brakes and couldn't bleed them. Still couldn't find any leaks.

Just as we were about to give up, my wife saw brake fluid dripping from
under the passenger floorboard. Pulled up the carpet, and yep, major mess.
The steel brake line there had rusted through and a small pinhole had
leaked massive amounts of fluid. Now I know where all that brake fluid was
going...

Anyway, I obviously need to replace the brake line, but it looks like it's
going to be a huge job trying to fish a hard metal brake line through the
car. Does anyone have any tips to make this job easier?

Also, I've got a major mess to clean up under the carpet now. Any tips on
cleaning up the brake fluid? I thought about spreading kitty litter all
over and letting it soak everything up.

Thanks,

Anthony