The plates just have to be correct for the year in New York State. There are websites that describe plates for different years. The ones for 1966 started a few years before then. They were blue with yellow letters, a small reflective tag was affixed as you renewed them from year to year. The stickers are not critical, as far as I can tell. You must have a matched set of plates for 1967.
The '74 were yellow with blue letters. I have two sets of those. I bought 'em for about $25. (I have a '75 Cadillac, but have never bothered to put the plates on it, mainly because I was letting the kids drive the car daily.) You'd be welcome to one of the sets for part of what I paid plus postage.
Poke around the internet for plate descriptions, and ebay to look for matched sets. I ended up outbidding a muscle car guy for the '66 plates I have, I paid $50 plus shipping. I didn't think much of it, I was happy to have the plates.