JDM engines and Smog laws

Desperately need some input on smog or what ever kind of restrictions the government puts on us. By us I mean the people who like the idea of buying a big ass motor from a JDM importer and puting it into their car to breath new life. I've been seeing some sites with disclaimers saying their engines are for race purposes only and to check with local laws before purchase. I can't find anything about smog or emission laws period!! Any insight would be appreciated. For specifics, I have the traditional swap intended: 94 civic 2 door with a GSR motor or H22.

thanks in advance