Offset for 1997 Z/28

I'm buying 18X9.5 ZO6 rims, they are replicas so they do fit the fbody. Problem is I have no idea what offset is searched and still not sure what will work.

50mm
65mm I know these are very small measurements here but I want it right, no fitment issues. Which one do I need?

i have the same size wheels with the 56mm offset

fit good

whats the difference between 50mm and 56mm will it create any problems?

6mm is like .5cm I don't see it being a problem. Am I right here or will there be issues?