With Gen2 Front calipers all around it might be two much rear bias even with a proportioning valve. Or there was some other Negative...i remember asking JonB about it. For the price that you can pick up used Gen3 Sets for i think you'd be better off going that route and using the BigBrakeDave adapter Kit(JonB now sells)
When its all said and done between the brackets calipers rotors proportioning valve, ect... your looking at over $1500
I was talking with JonB about every option and cost just a couple weeks ago. You should give him a call when you get back in the states.
I ended up choosing to save alot of $$$ and simply upgrade my rear calipers with the Tom's40mm Version. 700bucks and your done. Easy install too. Do SS lines while your at it since you have to disconnect the banjo fitting to swap the calipers anyway.
Some links for you:
40mmBrakes Home
Big Brake Kits 96-02