I've had several people email re the suspension/brakes for sale & whilst I don't claim to be an expert on braking systems here's my 2c worth.
The original GTD brakes are ford granada items mounted on GTD fabricated rear uprights/granada front. AFAIK a granada is way heavier than a GTD & has to be able to stop safely with four people on board, luggage, caravans etc etc... therefore (IMO) Granada brakes are plenty good enough for granadas!
Lots of people complain the standard GTD brakes are weak. When looking to improve the brakes, maybe it would be worth looking at the brake system as a whole, rather than focusing on the calipers/discs.
I beleive there is plenty of room for improvment in the GTD pedal box, M/C & servo setup. If you are at an early stage in your build it would be well worth looking closely at the pedal ratio & MC size. The GTD pedals are very short & a longer pedal could give a much better ratio. If you are using servos, make sure they are correctly plumbed, with the right type of vacuum hose.
Bear in mind that on a completed car, calpiers & discs are easy to change, they just bolt on! However, changing the pedal box may not be so simple.
Another key factor is cost. If you want good quality 'race' spec discs & calipers then consider a budget of around 2000 ukp. Consider doubling that figure (& then some) if you want ally uprights, rose jointed etc.
At the end of the day you pays your money & takes your choice, if you buy granada brakes for a few hundred pounds they'll be 'ok', but if you want a top spec race car/track day setup then you'll have to dig alot deeper! /ubbthreads/images/graemlins/grin.gif