I have an 8.5/3.73 gears in my 68 Camaro with about 200 miles on the gear set. It is noisy at about 30-40 mph. What are the chances of re-setting the gears after this many miles.

IMO, it's better for you to doit at 200 mi. than too late. At least you will end up reducing the noise and extending the life of the gear set anyway.

There is a chance that you might get it set right. I have had to correct other people's mistakes before and sometimes it works. Other times a new set of gears is the only answer.