But it is worth mentioning again, don't get fooled by "hp" ratings as the '70s progressed.
Yes, smog motors were down on power because of compression and cam profiles. However. In 1970 this was 'hp' rated in 'gross' terms, then we went to SAE net hp in 1972.
Gross hp, which for example was how a Chevy Chevelle SS LS6 engine was rated in 1970, was rated per SAE standards J245 and J1995. Corrections for temp humidity etc were in 'ideal' environments and the engines also were rated with little if any parasitic accessories such as a fan belt or a transmission. Many times long tube headers were installed. The test engine cited for the rating was also typically "one of the good ones"; they'd test a few and you can be sure they didn't select the lowest result. This as actually a type of brake hp, but with a stacked deck.
In '72 we swapped to SAE net hp, which comforms to SAE standard J1349, and while a trasnmission was still not part of the equation, belts and smog pumps etc were, and this test obviously lowers the rated numbers compared to SAE gross hp. If the same smog engine from say '73 were rated per the 1970 SAE specs J245 and J1995, the smog pumps and other accessories would not be robbing power.
Today we use what we call 'bhp' or brake hp, which is a slight confusion, as it seems we hadn't been using some type of bhp all along...so if we fast-forward to 2012, here's how Chevrolet touted the LFX equipped Camaro (boldface by me for emphasis):
"New, standard 3.6L “LFX” V-6 with
SAE-certified 323 horsepower (241 kW), which is 20.5 pounds (9.3 kg) lighter and helps maintain fuel economy of up to 30 mpg highway (2LS model)"
SAE certified means certified per SAE spec J2723 which is a validation of other SAE specs such as our old friends J1349 (from SAE net hp, above) or J1995 (from SAE gross hp, above). This does not necessarily mean an inflated rating for the engine, but it can mean some change from previous ratings.
So as you can see, bhp, SAE Certified, SAE gross and SAE net are all from various eras and are related but at the end of the day "400 hp" from 1970 is not quite the "400 hp" of 2014 and when you see a "200 hp" 455 from 1976, consider how many horses were negated by the changed SAE spec used to rate the engine.