There was a 454 big block V8 produced in 72. It had 365 horsepower.

The 1972 Chevelle SS had a top engine rated at 270 net hp (201 kW)

So, no, the LS6 was in 1970 with 450 hp.

The 1972 SS Chevelle 454 had 450 horsepower

1970 was the only year the LS6 454/450 HP was offered as a production car
there was also a LS5 455/360 HP version  Gross

1971 had 1 454 version, the LS5 rated 365 HP Gross

1972 again had the same basic  LS5 engine but now rated SAE, 270 HP