To me you are making it more complicated than it needs to be. If your axle casing is ok just fit the Wolseley brakes to the Minor axle but swop the brakes from side to side then you can use the existing Minor handbrake cables without any modifications.
The brake shoe lead is not effected as all you are doing in swopping the brakes side to side is transferring the lead shoe role to the other shoe. As the cylinder is floating the force/effort on the brake shoes is equalised. Whatever additional braking power is obtained it is an advantage to have.
I have had a variety of brake set ups on my Minor over the years and in my opinion the best balanced brakes I have ever had are as they are currently configured with the Marina disc set up on the front and the Wolseley 1500 8" brake set up on the rear.
The brakes on my Minor have had to work very hard over the years and they have never let me down or caused me any concern as to their effectiveness. The car will pull up very quickly with no hint of the rear wheels locking up or loosing surface grip and always stopping in a straight line.
Anyway it all works perfectly and I am more than happy with the set up.
As regards the diff - to fit the brakes you need to remove the half-shafts & hubs so an addition 40 minutes of work will see the diff changed.
Below is a drum off photo of the Wolseley 1500 brakes fitted to the rear axle of my Minor. To the right of the picture is forward.

- Wolseley 1500 brakes.JPG (1.03 MiB) Viewed 3844 times