On the left is Cheby 8 lug disc, and on the right EB drum. Accounting for the missing drum, the cheby stuff is almost exactly 1" wider. Maybe 1 1/8 if you want to be picky.

http://home.earthlink.net/~mattsara/bb/5lug-8lug.jpg

From EB drum, to just plain old Chevy discs its about 1 inch wider on each side as well, the splindles are just longer
I Had no idea about the 8 lug stuff though