for sure, compression, cam timing for starters. Then in '75 first generation catalytic converters(junk) limited exhaust flow.
The mighty 454 LS6 in 1970 made 450HP, of note it was not offered in the Corvette until '71 and with a drop in compression it was down to 425HP. But....... in '71 it was equipped with aluminum heads, along with stronger crank and rods. That was the end of the LS6, 72-74 the lesser LS5 was as good as it got in BB offering.
Also of note during that period was that in '73 HP ratings were calculated 'SAE net' as opposed to a 'gross' rating.