I make 5 or 10 springs a year; I make them almost exclusively from drill rod, usually 3/8 diameter and heat the rod red hot and hammer it to thickness. I anneal the material in wood ash and after filing and shaping and fitting, heat the material red hot and water quench. That leaves the metal brittle hard and I draw the temper to 740 F approximately in molten lead. In the absence of a high temperature thermometer, you can float a thin piece of steel on top of the lead and when the pot heats to the point that the metal is just transitioning from dark blue to grey, pull the plug and keep the spring immersed in the lead for another 2 to 3 minutes. Your biggest problem will probably be having a heat source hot enough. I use a cutting torch with propane instead of acetylene
cheers mooncoon