The EPA says you’re welcome.
And the great State of California would say, “You’re busted.” And you’d get to park it until it was restored to it’s OEM configuration… 
But once it’s old enough (I think it’s 25 years here) they don’t care anymore (I know that doesn’t make sense, but that is California now isn’t it.)… that’s why a '68 Karmann Ghia with a Subaru WRX engine stuffed into it sounds like fun.