James. Twin leading shoe sounds like a better idea than hydraulic. I have 3 A7s, they all have hydraulic, so I have 3 cars to rebuild the brakes on. If they were cable/rod, I could be driving them instead!
When a friend took his A7 to a local garage to have it converted to hydraulic, he gave them my number so they could contact me for advice. When the owner of the garage phoned me to ask what to do, I said don't do it. Rebuild the standard brakes completely, with brand new parts. He agreed and my friend didn't have the work done. I sold the hydraulic conversion for him, I should have kept the bits for myself!