What is the biggest engine i can fit in my 1979 nova?

its a 2 door coupe i was just gifted...my cousin says it can fit a 454 but i say 350 the biggest it will fit. its currently running on a 250 l6.which I'm fine with but for the sake of curiosity...also is their any way i can legally get a bigger engine. my dad says they are going to start smog checking older cars again...thank you very much the best and most complete answer will be rewarded their points