The last year for the T/A 455 was 1976. In '77 it was a 403 Olds in most of the Firebird Trans Am's but the Old English script 6.6 liter cars (they only came in black w/all the gold pinstriping) only came in a Gen-yoo-ine Poncho 400. These were also Hurst T-hatches cars, I think they did between 600-700 of them. MSRP in 1977 was $10,000. The one I had, my girlfriend bought it new and I bought it from her.
There may have been some COPO order cars for drag racers powered differently, but cars like that usually went to famous drivers. Royal Bobcat, a MI dealership like Chicago Nickey Chevrolet or Baldwin Motion Performance may have built some 455's for customers.