My experience is that a 15/16 master cylinder will do the job for your disc & drums. I personally found that rear proportioning valves are a waste of money. Thoroughly check for blockages in your front brake lines. I highly recommend the #3 stainless steel flex lines. FYI - Wilwood recommends no more than 1200 psi at their front calipers. I discovered that you can't always rely on the rear reservoir on your master cylinder to operate your front brakes. One way of checking is to put a plug in one of the ports and leave the line connected to the other, hit the brakes and see what moves...brake shoes or calipers?