Re: According to eBay
...crack open the case and look at the inside back face of the bucket...
The previous poster meant that you need to get a long Torx screwdriver (no. 10, I think) and loosen the screws at the back of the 1980's compact mac in order to slide the back case off (a.k.a. cracking the mac). They are about the depth of a compact mac (about 30cm long).
I'm sure that ye all knew that. I just want to avoid any unnecessary violence to old tech.