Whoops, here’s yet another fast street 455 with the 2802 cam.
This time in a heavy ’69 Le Mans convertible running 13.1s in the quarter with ‘71 #96 heads and log exhaust manifolds no less:
https://forums.maxperformanceinc.com...51&postcount=5
The 2802 cam is clearly capable in a street 455, it sure looks like it might be one of the best cams for moderate builds and at the right price.
The OP’s ‘67 Firebird convertible isn’t exactly a lightweight either, likely to weigh in close to 3800 w/o driver. My brother once owned a heavily optioned ‘69 Firebird 350 coupe with A/C, power discs, windows, steering and drivers seat weighing in at 3750 w/o driver.
Cam timing/installation - questionable and needs to be addressed.
Rocker adjustment - verify that the valves are not adjusted too tight holding them off of their seats.
Carb tuning - also questionable. You have a good carb.
Ignition timing - critical and not just the total timing but the timing curve itself.
General engine health - perform a compression test.
Valve springs - if they’re worn out that’s a performance killer.
I’d address the leaking oil pan and main seal, replace the valve springs and degree the cam while replacing the timing chain set. Then pay for some time on a chassis dyno with a reputable tuner in your locale. You don’t need to throw a bunch of money at it changing things for it to be a strong runner.