Forged front straight axles are often cold bent slightly for wheel alignment,a degree or two.Back when ,the steering arms on old Fords were heated red and bent this way and that way to clear a lowered axle.I don't know anyone who crashed because of it,but I bet a few might have broken or bent.
Before you try this,and it should be a good experience if nothing else,that axle needs to be absolutely secure as in perfect level and bolted down.I suggest securing the axle to railroad tracks.It might be wise not to use rails that are frequented by locomotives.Then you need a jig of some sort to check the king pin position accurately before any heating.Once hot you want to bring the axle ends in as alignment as close as possible the first time.
It's easy to apply two torches,heat it red where the axle end curves upward bend itwith a huge pipe wrench to a predetermined point you figured out before hand on your "engineered" alighnment rig.Now heat the top near the kingpin eye ,bending it down to the original angle.A strong pipe through the king pin holes helps also.This will narrow the front track some,it may or may not suit your situation.
As for stretching the axle? Red hot in an oven,forged on an Iron Worker machine into the shape you want.
