Early/pushbutton cars had a straight non-adjustable bar while later cars all had an arched non-adjustable bar for more bellhousing clearance. I suppose one could upgrade the stock bar (either type) by cutting it in the middle, welding in a steel slug that was threaded SAE left-hand on one side and right-hand on the other and adding a clevis (available from Pantera Parts Connection in Nevada, USA). To fully replicate Hall's commercial bar, you'd also need to weld in an extension at the correct angle for each end so it slid into the stock square pockets in the inner fenders. LOTS of (oxyacetylene) welding required. There was a recent post on one of the Forums that included a photo of exactly this mod.
Hall's all-steel bar is heavier than stock so I tried to reduce the wt while adding a clevis adjustment. I made my own adjustable bar from a commercial clevis and a piece of thick-wall 2" OD aluminum water pipe, pounded square on each end to fit the fender pockets. But even using a hollow aluminum bar TIG-welded as needed, fabricating my own jam-nuts of 7075 aluminum, cutting the clevis-hex down to the next smaller wrench size and gun-drilling a 1/2" ID hole in the threaded steel clevis shaft, my assembly was still 1.1 lbs heavier than a non-adjustable stock bar. Required a TIG welder, left and right-hand taps and dies, a lathe and 2 weeks of garage work. Depends on what you want, I guess. Good luck.