for whats its worth.
I consider rear disc breaking an overkill on a seven of any kind. The reason - the brakes need to be balanced for effective breaking - rear does not need that much - and in my case I have bias bar fitted. I also have a Sierra diff unit in the rear of my car Im building and used the hubs with drum brakes as is straight out of the Sierra. This is simple, cheap and save a lot of complications instead of going the disc way.
That said, the rear drums of a Sierra was design to haul down a car weighing about a 1300kg safely, and in a car such as a seven weighing about 600kg max, the drums are more than ample for the rear and would be operating at a fraction for what they were designed for.
BTW, a friend of mine races his car for the last 3 years successfully and runs drums at the rear and is not interested in changing to discs and to quote him, he does not have money to waste.
As for my car, I finally decided to install a Toyota 3sgte series 3 turbo engine that's on order, good for about 180kw, perhaps a little more since I am going to change the heavy cast iron exhaust manifold with a lightweight tubular one and I am comfortable of the braking power the Sierra drums at the back for such power.
Just my thoughts and perhaps many will disagree
