For the classic plates, anything 1975 and older needs to pass emissions once and then you're good after that, plates are 5yr plates at a time.
Anything 25 or 30 yrs (can't remember which one) or older (1976+) can get collector plates but have to pass emissions every 5 yrs.
Not sure why, but every time I take the Comanche in, they crawl all over it and check EVERYTHING (it's always passed). They barely look at my other vehicles, lol.