Stock Mini rear brakes are already too much. That's why a pressure reduction valve (proportioning valve) was standard even on disc braked cars.

Kelley

Yes, too much brakes on the rear of a Mini is not a good thing!

Not only would twin leading shoes be the exactly wrong direction to go in at the rear...make sure that disc brakes up front are matched with a narrower bore rear wheel cylinder (5/8"/0.625 in.)..otherwise your rear wheels will lock up and you will do a tail swap in the wet or on dustry road surfaces.

Excellent info, forgot about the handbrake!

The backing plates are also different. The backing plate for twin-leading brakes does not accommodate the hand-brake linkage.

The brake drums are the same size front and rear, unless you have spacered drums, but the brake drum itself is the same width. The rear brake shoes are more narrow than the front brake shoes however.

Apart from not necessary IMO, stock rear drums are narrower than the front so can't be done anyway. 

Any advice on putting disc brakes front, twin leading shoe rear brakes? Is that too much braking at the rear? Seems like it would be an easy conversion...........