its light but it maybe N564512

N6 is OK. The next digit is the problem.... probably a 6??
Look like N664512?

After closer inspection it looks like -N684512

DZ blocks take forever to sell and nowhere near 4K. Had 3 over the last five years. Not much value except if you find the the original car, as has been said, then who knows what that person will pay you for it. eBay and the various chevy & Camaro classifieds are littered with them. Seems they are slowly becoming conversation pieces and garage art?