I have done a couple set of headers out of copper wire it bends real easy! and if you misbend it grab another piece. Solder works well also the 125 diameter is good for big blocks use the solid wire solder. The ones with a "core" the flux will leak out over time and wreck your model! K & S alum. tube works very nice one trick I've learned put a piece of Evergreen tube inside as it will support the tube as you bend it and will not colapse and if you are doing side pipes you can grind the Evergreen out sometimes you can pull it out. HTH PK