Just reinstall the ABS system, as 50/50 bias can be a handful on track and dangerous on the road. Can't really add a bias valve to the abs system as its still running through the ABS pump with individual lines.
Options are 172 cup set up or 172 cup master cylinder, custom lines and bias valve. You'd find all the above on ebay, but by the sounds of it a garage would need to install it which starts getting pricey.
Options are 172 cup set up or 172 cup master cylinder, custom lines and bias valve. You'd find all the above on ebay, but by the sounds of it a garage would need to install it which starts getting pricey.