I just bought a 93 K3500 with a blown head gasket. I only paid 1500$ for the truck! That's the good part.
Here's the bad part. I bought 2 new heads and installed them, then as I was reinstalling the injector lines, I noticed that one of the #1 injector line's hold down straps had come loose and "sawed a slice" into the line. It still held pressure when I tore it down, evidenced by the fact that the line was perfectly clean. No diesel-spill-fuzz built up on it at all.
Here's the deal: I have a spare injector line from a 6.2 engine, but I noticed that the internal diameter is smaller than the 6.5 line. Can I use the 6.2 line without causing rough running?
I think I already know the answer, but I thought I would ask anyone here with more experience than I.

Actually the biggest problem is the angle of the injectors. The 6.5 injectors are more verticle in the heads to clear the turbo manifold. The 6.2 heads have the injectors tilted down a little bit. The injector lines are shaped a little bit different because of the injector angle. I have seen people use the 6.2 injector lines on a 6.5 without any problem other than having to bend the crap out of the lines to make them work.

I can not really comment on the inside diameter of the lines, I do not know if it matters or not.