If it is still in a solid piece, even if rusted, you can usually bend them back into shape & keep them. If it is trashed, I can probably point you to some mods that people did to keep the old bucket with the newer style ash sweeps with the washer with the H-shaped opening.
If your replacement sweeps are the newer style sweeps & the bar is salvageable, you can do this mod that requires no alteration of the leg sockets on the bowl or of the bucket holder.
@toolhead came up with it & it is pretty darn easy. You just need a little cheap round file. If you don't have one already, you can pick up at Menards, Harbor Freight or other places. See this thread and the one that Toolhead references in it.
http://weberkettleclub.com/forums/index.php?topic=42723.msg428581#msg428581If you don't already have sweeps, you might consider doing a search to find the part number for stainless steel sweeps so that you don't have to bother with it in the future.
If the bar is gone, there are a couple other mods that will allow you to use the old bucket. Some required drilling the leg sockets on the bowl. The one I was going to try (before finding Toolhead's solution) was one that only required drilling the ring that holds the ashpan, but nothing on the bowl itself. Let me know if your bar is completely trashed as I could probably find that one fairly quickly.