vw1303, you may want to do what the Porsche guys have done. The early 944 master cylinder doesn't have a proportioning valve but the later cars do. They take the late 33/5 proportioning valve and add it the early master cylinder. The part number is 928.355.305.02 and costs about $70 but it isn't adjustable like the Wilwood unit.

There are also a few other things to take into consideration. Make sure that you have the lines connected correctly because the 944 m/c is opposite then that of the 1303. This meaning that on the 944 m/c it has the front hole for the rear line. Have you checked this? If not, start there first.

There are also other options but try the above first. Porsche also used a 18/5 proportioning valve on the 944 but it was replaced with the 33/5 eventually. Also, some 944 owners have put a 23mm Mercedes Benz master cylinder on their cars but I have no details about that conversion.

Some other things to think about is if your rear tires are much larger than the front and/or if the car is lowered in the front. These can affect bias as well.