How it usually works is the vehicle is smog checked for the year of the vehicle not the year of the engine in the vehicle. Most states have a rolling 30 year cutoff point for checking for smog. Reason being is such vehicles are collector / special interest cars and dont get driven much, and are usually in a good state of tune to bother with smogging them.
My dad had an initial inspection on his 79 dodge lil red express truck after we rebuilt it, this was in new Jersey, after that since he has QQ historic plates on it, he renews registration, and keeps insurance up on it, no inspection since.
Check your states laws regarding classic cars, smog checks etc.