090,
yes you can enter two classes but just be mindful that races will be running back to back so if you thinking about entering era's that run back to back, it may be a challenge. But if you entered say Pre 75 era and Pre 85 era, you would have the Pre 80 era race in between to recover/re-group and get to the line. All depends on how fit you are feeling but you most certainly can enter more than one class. Cheers.
Dan