A: Helping you find headers will help every other Camaro owner out there. You're correct that a Camaro header will fit your Firebird, and at least you're putting a real engine into your Tin Indian!
The Hedman tech was correct in its assumption that the corners of the standard street header may blow out the header gaskets. However, in the Hedman Hustler line of racing headers there's a great one for your application. We use the same Hustler line on our Malibu wagon with LT4 heads that have the same D-port exhaust. Hedman offers these headers for the Camaro in either 15/8- or 13/4-inch primaries and 3-inch slip-on collectors. We'd recommend going with the 15/8-inch header, PN 65018 (the 13/4-inch are PN 65019). This header will fit with power steering. They will not fit with A/C. Hedman specifically points out that these headers will fit with raised exhaust ports, and angle plug heads.
Good luck with your project. If you would have started with a Camaro you wouldn't have had any problem. Well, maybe so, but enjoy your new powerplant.
Technical questions for Kevin McClelland can be sent to him at email@example.com.