There's a lot of confusion about the various 'valves' and stuff that were in the brake systems on these cars. It didn't help that GM did different things in different years. For front disc cars in some years there was a hold off valve, a proportioning valve, and a distribution block/valve. The hold off valve's job was to prevent the rear brakes from locking up before the front brakes were working. The proportioning valve balanced braking action between front and rear, and the distribution block's only function was to act as a switch to detect a pressure imbalance between front and rear and turn on a light if one was detected. It's main job was to alert you to the possibility of a leak in either the front or rear brake system in cars that had dual master cylinders. That's the brass more or less rectangular block that mounts down low on the inside of the driver's side frame rail and has a wire connection "in the middle". The distribution block/switch works off of brake line hydraulic pressure, which is considerable - so mounting it at an angle instead of "flat" shouldn't be a problem if that's what you're asking.