can you weld? if so mark a straight line along the axle tube each side (for alignment). then cut out the required amount in the middle of each tube. now clamp the end sections to the centre (aligning the straight line) between 2 pieces of angle iron. this will hold the tube dead straight while you tack the tubes together. then fully weld switching to opposite sides of the tube to avoid distortion. i've done many axles this way as have others, when the shorter axles are refitted they always spin nice and free with no hint of tightness so.....
neil.