'75-76 Dart Sport 360, why hp so high?

GM's X-bodies small blocks couldn't get above 200 hp net from 1974.......even Mopar's 1975 top-tune 400 ci Road Runner had just 5 more hp than Dart Sports 230hp.

Which makes me wonder if Mopar delayed installing catalytic convertors on this car until 1977? Does any FABO member know the reason why Dart Sport (and Duster) 360 hp hung on so high for so long?

Thanks, Kellen