I can help you here. I've made one.
Bar is round stock, 1-1/8" to 1-1/4", I used T-GAP shafting(Turned, Ground, And Polished). You then need to machine steel or aluminum "pucks" to go in place of the carrier and axle bearings that have a hole the size of your shaft through the middle. Once the carrier bearing replacement pucks are placed in the housing and the rear caps installed the bar is placed through the housing. Then put the axle bearing pucks in the housing ends and slide them onto the main shaft. This way all the bearing bores are kept in alignment. Be sure to align the axle bearing ends before welding so the brake cylinder bleeders will end up at the highest point when the axle housing is in the car.