"Rocket" doesn't mean much. It was the style in the 50's and 60's to put wild names on mundane iron. Like Super Stud Jetfire Nuclear Blaster Weapon of Mass Destruction on a 7-1 compression 194cid six-popper.
Those pre-'72 engine ratings don't mean anything either. 400hp and 500ft# on a 455? The Pontiac Superduty in '73 made 395ft# NET and was a seriously bad-ass car--running the quarter in the 13's at around 105mph from the factory floor. Most 'pre '72 engines, like the old 460 that I got out of a '71 Lincoln and installed in my '64 Galaxie-and old 440s and 455s, were in the 350ft# NET range and were advertised in the 500ft# GROSS range. My '64 with the '71 460 with the compression reduced to 9.8:1 so it could run hard on pump gas, and with a Ford Motorsports cam on a straight-up, Performer intake, AFB carb, electronic ignition, 3.0 gears with an open axle and a C6 ran 5mph slower than a SD TA at 3800#.
I didn't mention horsepower because horsepower is easy to get by spinning the motor faster. Torque is tough because you need more air per cycle to get it--horsepower just need more cycles.