Bob, first off have a look at a post started on July 20 @ 08:30 by CCWKEN titled "Stanchion Mount - How much is missing?". It has some good pictures posted by others of the Cowl Posts, the Belt Rail, brackets, etc.
The piece across the top which ties the cowl posts together is part #A-35355 (Front Belt Rail) I believe for the 28-29 open cars and trucks - the "and reinforcement ***'y" which Dennis refers to above was included in the name of some of the closed cars - tudors, coupes, etc. This is what you likely already have as it joins the cowl pillars together. I'm not sure what the correct name for the finish panel (what you probably need) is - possibly A-35360 (Front Belt Rail Finish) - it is attached by 6 screws - 2 on each end @ the cowl post brackets, and 2 in the middle using "L" shaped brackets and two of the same holes that go thru the belt rail and the gas tank.
The terminology you've used (Dash Rail and Dash Bar) is used by some suppliers for sure - Brookville Roadster calls the two pieces A-1001-A (Open car dash RAIL) and A-1005-A (Dash reinforcement BAR). In their words the latter "ties the cowl posts together". So using their terminology what you are likely missing is the Dash RAIL.
Hope this helps some and hasn't been too confusing!!