I have been a Buick guy for a long time, and have never seen a header for a Buick 455 installed in a Trans Am. The only vendor I know of that sells Buick headers is T A Performance in Scottsdale, AZ. If your current shortys were bought and not custom made, this is where they likely came from. I had their shortys on my 72 Buick Gran Sport, which is an intended application for them. But, I still had to dimple one tube for steering shaft clearance. I would venture that the shortys you have now are your best option, short of having a custom set of headers made.