I just found these wilwood bias valves on ebay , just purchased one , 40 quid plus postage cheapest ive seen.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=320492607181&ssPageName=STRK:MEWAX:IT

Won't work on your car the hydraulic line pressures are too low,

If i change the rear drums for discs i need to reduce the pressure.I was going to use a mondeo valve but dont know if it will be to lttle or to much reduction.

I went for the bias valve as i assumed it was the standard solution to reduce rear braking, not sure what to do now.