I will be swapping from the stock 6 cyl rearend to an 8". The brake line from the 8" is trashed. Can I take the metal brake line that ran the length of the 6 cyl axle and use it on the 8"? It will hook up to the 8" master cylinder?

 

When I did the swap, the point where the two lines meet on the rear is 2 1/2 inches further left so the old lines would not work. When you buy new lines there are two options for the 8" rear (single exhuast, and dual exhaust). Check out this article about the position of the rear brake hose if you are running duals on a single exhuast brake line setup.
http://www.karmustang.com/dual_exhaust_conversion.php

 

aye ... wdual exhaust needs different setup than single exhaust. you don't want to heat your brakelines.
if you check on NPD etc there are readymade kits available, or get a flaring tool, a few meters of brakeline and do it yourselves ..

 

i agree on the ready made kits. i have to replace all the hard lines just to replace the soft lines (fused together after 43 yrs haha). I figured the $90-100 for the ENTIRE cars hard lines pre bent was well worth what ill save in fraustration

 

I want to replace just the rear hard line (rest of the lines are Ok)
Will the 6cyl hard line mate with the new V8 hard line? Will my 6cyl line mate correctly with the junction block on the 8" axle?

 

Take a piece of coat hangar and mock up a line from where your old one stops to where you want to end so that it fits your new rear end's flex line. Then measure it and go to Autozone and buy a stick of brake line with the inverted flare fittings already installed. You'd also need a 3/16" union to joint the two together. Then buy you 5.99 tubing bender from harbor freight and form the line to your mockup. You'll have to use some type of gromments or line clamps to secure the line extention.

Hard to see in this photo, but you can see how I made an L bracket to hold the mating of the line and hose. just above the pumpkin in the photo.

http://midnightdsigns.com/james/images/Exhaust3.JPG