Hi Carl, I have been wondering how that dome car project has been going. I have been watching your original thread because I wanted to see how you tackled this problem.
The biggest issue with that 15" dome structure is it doesn't look wide enough to fit your shell. From the photos at the top of this thread it might be 1/4" to small to fit the width of your car. It would be real tough to fabricate something that could make up the 1/4" difference and still match the roofs rounded surface. From what I remember of your original posting you needed a 6 1/2 long by 2.5 wide dome structure and matching window? If that's true those are the exact dimensions of a K-Line dome car (as seen in the photos below). So the first thing is to verify that 15" dome structure has either a width of 2.25" or 2.5". Next is that 15" dome structure looks more like an ACF dome than Budd but that's a minor fix.
Easiest option: Since there are no train shows to find used shells right now, you could buy the K-Line shell with complete dome section that's on eBay. It has the correct Budd style dome structure you want, includes the inside dome window. If you can verify it matches your dimensions all you would have to do it paint the dome structure the color you need. Here's a link: https://www.ebay.com/itm/62013...1:g:3WoAAOSwfl1ciofM .
Find an inexpensive kit that includes a brass dome: Wait for more 21" MAC shop dome cars to appear on eBay. 3 of these MAC shop dome cars sold last month for $24 each. Each MAC shops car included a complete brass dome structure that gets built to the exact length needed. Also, since it came from a 21" MAC shops car there is a better chance this brass dome will match the width of your car. https://www.ebay.com/itm/DR-P1...rksid=p2047675.l2557
Although, Brasseur Electric Trains do not have replacement K-Line domes anymore, they do show different size replacement glass sections which could help if you were to fabricate your own dome: https://traindoctor.com/servic...ages/K4688-03-03.jpg
Let us know what you decided 
