71 383 - options

This is what I discovered.

HP for 1971 means High Performance, labeled a Magnum or Super Commando engine, for a 1971 Road Runner/'Cuda/Challenger/Charger/Super Bee, with a Holley 4 barrel, 8.5:1 compression, 300 gross horsepower, 410 gross torque.

Basically, HP was for the engine in the super cars of the day, not granny's station wagon.

It also seems to make sense what Allpar has listed regarding the crank, that starting in 1971, the cast iron 383 crankshaft was used as a cost saving measure on automatic-transmission cars.
HP or not, in 1971, a forged crank was used if it's for a 4 speed. The chart on Allpar shows the 1971 383 had a Holley 4 barrel and was standard in the Road Runner and 'Cuda. Only year for gross and net numbers.

1970 had two HP 383s, both with 9.5:1 and a four barrel, one with a Holley. There was also an 8.7:1 non-HP 383 with a two barrel.
1971 had one HP 383 with 8.5:1 and a Holley 4 barrel. There was also a two barrel non-HP 383 with the same 8.5:1.
Starting in 1970 compression was lowered, to cut back on emissions, and to run on regular gas, meaning lower octane gasoline, not unleaded fuel.
Starting in 1973, exhaust-valve seats were induction-hardened to allow use of lead-free fuels.