1974 - 904 Transmission Reverse/Low Band - ???
Hate to disagree with you, but according to my parts catalog, and looking at the W.I.T. Parts catalog, the 904 and the A500 do use the same double wrap band.
I had to use the catalogs, as it's been a while since I worked selling transmission parts and converters.
It appears that you live in UTAH, and I'm sure that there will be a TRANSTAR transmission parts warehouse there. Check with them.
Just did a quick search for you. Transtar has a warehouse in Salt Lake City.
I should point out that the bands sold by Transtar or like transmission parts suppliers are the same bands you'd buy from CRT. CRT doesn't make bands. They buy them from manufactuers like Raybestos or Borq Warner.