header length...

I just got a pear of long tube headers for my 80z and i was just wandering how much longer are they then the stock 350 headers under the car??

uh, stock the car came with cast-iron exhaust manifolds. Probably don't extend much below the cylinder head, while most headers will extend to somewhere behind the engine...
You're in luck though - Jegs makes a set of short pipes for hooking up headers to an existing exhaust system. They will bolt onto the end of the headers, and there's a slight 'S' bend to allow you to line everything up, then just cut off the current pipes at the right spot and weld everything up