Hi Milo
I am not an expert on Social Welfare entitlements, so this is just an opinion. Your best bet is to call into your Social Welfare office and they will help you.
If you are being asked to cut down work because of lack of business, you will be entitled to unemployment benefit if you have made 39 A contributions in the year 2001. If the short time work begins in 2004, the basis year will be 2002.
Are you sure you are Class B? I think that is for some public sector employees. Do you work in the public sector? If so, the B contributions wouldn't entitle you to unemployment benefit.
As I say, don't take this as gospel - check it out with your social welfare office.
Brendan