self larnin' goin' on--narrowing rear axle

you Could ask for some tubing as thick a wall as possible. Of course it should be straight.
(sounds nasty dont it..) Look at it first b4 u buy it. If it slightly bent it can be straightened. (Axles get straightened and so do cranks.) Solid round bar is way expensive; yes a solid round bar that is wide enough to do both sides at one time would prolly be more accurate, depends on how much U wanna spend and if u can get the steel cheap, like from a scrap yard. If you go with new, tell em what ur doin and they can steer u in the right direction as far as tubing. A 5' length of thick wall tubing is not going to be bent that much unless it has taken some serious abuse. If it did they prolly wouldnt be able to sell it.