I'm installing an SSBC proportioning valve as part of a disk brake upgrade to my 71. I'm trying to figure out which size adapters I need to fit the valve right where the rear brake line comes out of the back of the stock distribution block. The threads on the nut look to be 1/2 or 9/16 fine thread but I can't really tell without unscrewing the fitting and getting fluid everywhere. Anyone else ever do this? Any idea what size the tube nut going into the dist. block is?