Modern clutch release bearings look different from the original ones fitted to the classic Mini. Despite the different appearance of current production from the early type that these now replace, they are a press-fit onto the release plunger just like the early design, and perform identically. Ref: GRB238, GRB201, CCT38.
For performance use, see GRB0238HD bearing, which has integral metal oil seal instead of plastic, as supplied by AP Racing in their 3-piece clutch kits.
If your engine has a clipped-on "floppy" release bearing, then you probably have an A+/Metro power unit, which uses the GRB0239 bearing instead.