I just got through heat treating a long, thin sword blade. I did it with a converted BBQ grille. I just laid a perforated pipe in the bottom and hooked up a vac. I built a coal fire and it afforded an even enough heat that I was able to harden the blade. After than I drew temper in an oven at 550 degrees. What I got was an extremely tough, resillient blade that would be next to impossible to break.
-PS If there is some minor warpage, don't worry too much about just yet. I think some warpage is almost inevitable in a blade of that size and, even though it was extremely springy, a few square whacks with a heavy hammer while the blade was still hot from the tempering process pretty much straightened everything out. Just remember if you're going to try to cold-forge any warpage out, go easy on it and do it after the TEMPERING! If you do it after it comes out of the quench chances are it will shatter.