You should replace the camshaft bearings every time the block goes to the machine shop. These bearings fit all late model 1275cc blocks (the ones without tappet covers on the back) It's almost too simple and thus often overlooked during a rebuild. Camshaft bearings are pressed into the block and thus are usually done by a machine shop. You would not rebuild an engine without replacing the rod bearings, so why not the cam bearings? Minis have one of two sizes of cam bearings; blocks with tappet covers use
AEC3046 those without tappet covers (ie Austin America) plus all Cooper S use
AEC3063.